Support and validate CPython 3.14

[lopezm1]

Summary

Add and validate CPython 3.13 and 3.14 support for the Python SDK without changing feature-flag evaluation semantics.

Confirmed compatibility blockers

• Package metadata currently rejects Python 3.13 and newer with python_requires="<3.13".
• The declared urllib3>=1.22.0 floor permits releases that fail to import on CPython 3.14. urllib3==1.26.5 is the first compatible release in the tested 1.26 line.

Proposed scope

• Extend tested package metadata through CPython 3.14 (excluding free-threaded 3.14t).
• Raise only the urllib3 minimum to 1.26.5; keep all other runtime dependency constraints unchanged.
• Add blocking CI coverage for Python 3.13 and 3.14 plus an exact-minimum-dependency job on 3.14.
• Build and install the wheel in a fresh Python 3.14 environment, run pip check, and exercise the public offline client API and shutdown lifecycle.
• Update the README and release metadata for 1.1.9.

Acceptance criteria

• The full existing suite passes on CPython 3.12, 3.13, and 3.14.
• The exact declared runtime minimums pass on CPython 3.14.
• The built wheel installs and passes pip check in a clean CPython 3.14 environment.
• Public API evaluation, caller defaults, listener removal, repeated evaluations, and idempotent shutdown pass without leaked SDK worker threads.
• No evaluation, targeting, context, default, networking, event, lifecycle, shutdown, or public API semantics change.

This repository is the FeatBit SDK layer. Validation through an OpenFeature provider remains a downstream provider responsibility.

@dsun0720, feedback on the compatibility and release scope would be welcome.