fix(pytest): execute import hook before conftest.py files are read

[jeertmans]

Hello!

This comes a bit out of nowhere, but I had this bug for a long time where running pytest on specific paths (instead of the plain pytest command) would raise an error because my package would already be imported, before the import hook could be run.

After some research, I found that the issue originates from my contest.py files, which import the package under test to create fixtures.

Apparently, this issue can be fixed by changing how your plugin is run, i.e., by evaluating it during the initial phase. I looked at other projects, and this seems to be a common practice.

Here is a small patch for this purpose :-)

You can verify that it works by adding import equinox to equinox/tests/conftest.py and then running pytest.

[patrick-kidger]

LGTM! Thank you :)