Add spatialindex version to tests, add common pytest configuration

[mwtoews]

This adds a common module for the tests, for items that aren't fixtures. So far it gets the libspatialindex version string and tuple.

Also establish a pytest configuration.

[adamjstewart]

Wouldn't it make more sense to define this as a reusable fixture in a conftest.py file? https://docs.pytest.org/en/stable/reference/fixtures.html#conftest-py-sharing-fixtures-across-multiple-files

[mwtoews]

Aren't fixtures specific to running pytests? I.e., shouldn't sidx_version be just a regular variable? I generally keep conftest.py only for fixtures, not other variables.

Also, it seems that I don't know how to stop deploy from always running, despite adding a "paths" filter for pull_requests.

[adamjstewart]

Yes, fixtures are only compatible with pytest, not unittest. They can be used for anything that needs to be repeated in multiple places.

For deploy, I think the change will only go into effect once it is merged, you can't enable/disable workflows on PRs.

[mwtoews]

I can't see an easy way to leverage fixtures as simple variables (since fixtures are special functions), so will proceed with a simple approach in tests for now.

For 1.5.x, both sidx_version_string and sidx_version cam be moved to the main module, as these could be handy for users too.

Just noticed that the conda tests were always excluding macos and SIDX 1.8.5, which is fixed to cover these.