Add a GitHub Action to run pytest

[cclauss]

Test results: https://github.com/cclauss/kokoro/actions

@danielzgtg Your review, please.

[danielzgtg]

• Python 3.9 does not work: https://github.com/danielzgtg/kokoro/actions/runs/17345822812/job/49245655329
• None of the Python 3.10, 3.11, 3.12 tests in that run succeeded
• Python 3.13 is blocked on waiting for a version of misaki containing both my PRs to be published to PyPI
• Python 3.14 isn't released yet

[cclauss]

Python 3.14 is in release candidate 2, and the Python Core Team requests that developers test it to provide feedback before it is finalized in October. Ensuring that it passes tests is not the same thing as supporting it, but it is quite close.

Any ideas on the failing tests on Py3.10 thru 3.12?

[danielzgtg]

I don't know. I tried reverting e43d626 and resolving the conflicts, but just got a similar test_stft_reconstruction error with different floating-point numbers in the second tensor. /tests/ might be unmaintained as there's only one author.