* Update tox.ini for newer file format and new Python versions

* Update GitHub Actions workflow to use newer Python versions

* Update GitHub Actions versions

* Specify GitHub actions Python versions as strings

* Fix race condition causing intermittent gzip corruption

The _process_chunk method checked _last_chunk to determine whether to
use Z_FINISH, but _last_chunk wasn't set until after the read thread
submitted the final chunk. This caused the last chunk to sometimes be
compressed with Z_SYNC_FLUSH instead of Z_FINISH, producing invalid
gzip files with unterminated deflate streams (00 00 FF FF marker).

Fix by peeking ahead in _read_file to determine is_last before
submitting to the pool, and passing the flag directly to _process_chunk.

* Update tests to reflect passing in is_last to _process_chunk

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

* Update how package gets version metadata

* Add pyproject.toml