Updating zarr-python for free-threaded CPython

[nenb]

It was pointed out to me today by @tpn that the upcoming free-threaded CPython will likely be a huge boon for workloads that involve loading large data structures in parallel i.e. zarr-python workloads.

At a very basic level, I'm not sure if zarr-python is compatible with free-threaded CPython in its current state. If not, this will require work to support.

And more generally, I'm sure that there are areas of zarr-python that can be updated to benefit from the improvements to CPython. I'm creating this discuss as a location where folks can suggest areas of the zarr-python codebase that can be updated to benefit from the CPython improvements.