Remove backports datetime fromisoformat

[eprbell]

This is an attempt to address #273.

The backports-datetime-fromisoformat package no longer installs (see the issue for a full description). This package is only needed for Python < 3.11, so I removed support for older Python in the setup file and I removed references to backports-datetime-fromisoformat from the code.

Unfortunately tests test_plugin_ccxt.py and test_plugin_ccxt_exchangerate_host.py no longer work. They fail with:

Traceback (most recent call last):
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/runner.py", line 341, in from_call
    result: TResult | None = func()
                             ~~~~^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/runner.py", line 242, in <lambda>
    lambda: runtest_hook(item=item, **kwds), when=when, reraise=reraise
            ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_hooks.py", line 513, in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_manager.py", line 120, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_callers.py", line 139, in _multicall
    raise exception.with_traceback(exception.__traceback__)
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_callers.py", line 122, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/threadexception.py", line 92, in pytest_runtest_call
    yield from thread_exception_runtest_hook()
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/threadexception.py", line 68, in thread_exception_runtest_hook
    yield
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_callers.py", line 122, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/unraisableexception.py", line 95, in pytest_runtest_call
    yield from unraisable_exception_runtest_hook()
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/unraisableexception.py", line 70, in unraisable_exception_runtest_hook
    yield
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_callers.py", line 122, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/logging.py", line 846, in pytest_runtest_call
    yield from self._runtest_for(item, "call")
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/logging.py", line 829, in _runtest_for
    yield
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_callers.py", line 122, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/capture.py", line 880, in pytest_runtest_call
    return (yield)
            ^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_callers.py", line 122, in _multicall
    teardown.throw(exception)  # type: ignore[union-attr]
    ~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/skipping.py", line 257, in pytest_runtest_call
    return (yield)
            ^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_callers.py", line 103, in _multicall
    res = hook_impl.function(*args)
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/runner.py", line 174, in pytest_runtest_call
    item.runtest()
    ~~~~~~~~~~~~^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/python.py", line 1627, in runtest
    self.ihook.pytest_pyfunc_call(pyfuncitem=self)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_hooks.py", line 513, in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_manager.py", line 120, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_callers.py", line 139, in _multicall
    raise exception.with_traceback(exception.__traceback__)
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/pluggy/_callers.py", line 103, in _multicall
    res = hook_impl.function(*args)
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/_pytest/python.py", line 159, in pytest_pyfunc_call
    result = testfunction(**testargs)
  File "/Users/marcoz/prj/experiments/dali-rp2/tests/test_plugin_ccxt.py", line 50, in test_build_fiat_list
    plugin._build_fiat_list()  # pylint: disable=protected-access
    ~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/Users/marcoz/prj/experiments/dali-rp2/src/dali/plugin/pair_converter/ccxt.py", line 207, in _build_fiat_list
    response: Response = self.__session.get(_EXCHANGE_SYMBOLS_URL, timeout=self.__TIMEOUT)
                         ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/requests/sessions.py", line 602, in get
    return self.request("GET", url, **kwargs)
           ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/requests/sessions.py", line 589, in request
    resp = self.send(prep, **send_kwargs)
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/requests/sessions.py", line 703, in send
    r = adapter.send(request, **kwargs)
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/requests/adapters.py", line 667, in send
    resp = conn.urlopen(
        method=request.method,
    ...<9 lines>...
        chunked=chunked,
    )
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/urllib3/connectionpool.py", line 787, in urlopen
    response = self._make_request(
        conn,
    ...<10 lines>...
        **response_kw,
    )
  File "/Users/marcoz/prj/experiments/dali-rp2/.venv/lib/python3.13/site-packages/urllib3/connectionpool.py", line 551, in _make_request
    response.version_string,
    ^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'VCRHTTPResponse' object has no attribute 'version_string'

@macanudo527, any thoughts on the test failures?

[eprbell]

The issue has been resolved in backports.datetime_fromisoformat, so this is no longer needed.