feat: simplify pytest plugin

[adhtruong]

Description

• This PR simplifies pytest plugin and improves ergonomics of usage
• Current implementation returns the pytest fixture then uses a registry to expose usage.
• The new implementation injects the fixture into the caller scope so the returned object is the factory itself. This allow direct usage of factory and simplified usage

Closes

[provinzkraut]

Looks good but this is a breaking change, right?

[adhtruong]

I'm on the fence. This is changing the return type of register_fixture but only documented or productive use of this would be with Fixture field. I've preserved usage of Fixture field itself and deprecated that instead so existing code should work based on tests using a registered factory with Fixture field.

In terms of fixture naming and scoping with respect to pytest, this is also preserved

Edit: also worth noting the return type of Callable[[], type[T]] is largely wrong. This returns a pytest fixture so

from dataclasses import dataclass

from polyfactory.factories import DataclassFactory
from polyfactory.pytest_plugin import register_fixture


@dataclass
class MyModel:
    values: int


@register_fixture
class MyModelFactory(DataclassFactory[MyModel]): ...


print(MyModelFactory())

will raise the following error

Failed: Fixture "my_model_factory" called directly. Fixtures are not meant to be called directly,
but are created automatically when test functions request them as parameters.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/polyfactory-docs-preview/652