chore: declare Python 3.14 classifier

[ltsyk]

Summary

Declare Python 3.14 in package classifiers (tox already lists py314; issue #793).

Fixes #793

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[ltsyk]

Removed the accidental tox.ini.bak that snuck into the branch; the PR now only adds the 3.14 classifier (and the intentional tox.ini envlist update).