add py315 rc2 (except for wasm) to ci/pyproject.toml

[AndrewAnnex]

Oct1st is pending release date so likely can get things a bit situated ahead of the release.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.61%. Comparing base (acfb3c6) to head (4bf8642).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #575   +/-   ##
=======================================
  Coverage   99.61%   99.61%           
=======================================
  Files          19       19           
  Lines       18094    18094           
=======================================
  Hits        18024    18024           
  Misses         70       70           

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