chore(main): release 9.15.0

[github-actions]

🤖 I have created a release beep boop

9.15.0 (2026-01-29)

Features

• Drop support for python 3.9 (#393) (5b761bd)

Bug Fixes

• Add context manager for clearer, safer locks (#396) (beca0fa)
• Address potential race condition in FeatureStore update_availability (#391) (31cf487)
• Prevent immediate polling on recoverable error (#399) (da565a2)
• Redis store is considered initialized when $inited key is written (e99a27d)
• Stop FeatureStoreClientWrapper poller on close (#397) (468afdf)
• Update reason documentation with inExperiment value (#401) (cbfc3dd)
• Update Redis to write missing $inited key (e99a27d)

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Note

Low Risk
Release-only metadata and documentation updates; no functional code changes are included in this PR.

Overview
Publishes the 9.15.0 release by bumping version metadata across .release-please-manifest.json, pyproject.toml, and ldclient/version.py, and updating PROVENANCE.md’s verification example.

Updates CHANGELOG.md with the 9.15.0 entry (Python 3.9 support dropped plus several concurrency/polling/Redis-store related fixes).

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