Prepare Python SDK 2.3.6 cache release

[rmcdaniel]

Release

Prepare the stable Python SDK 2.3.6 patch for #84. This PR updates the package/product-train/registry versions and changelog after the cache fix merged at e3c5baf9bb40c3dd279bfdeae0eceb3d9edd5991.

Qualification before tag

• Cache fix PR Keep larger verified payload replay sets in Python cache #85 passed current-head Python 3.10/3.11/3.12, lint, integration, package, regression-corpus, docs and public-boundary checks.
• Candidate-source replay on published Server 2.4.26 completed the 1,000-external-signal fixture correctly with one GET per payload, no errors and no backlog.
• This release PR's current-head CI run passed, including package, integration, Python 3.10/3.11/3.12, lint and regression-corpus checks. Docs and public-boundary checks also passed.

After publication

Verify immutable tag, PyPI wheel/sdist and metadata, then repeat the fresh-worker fixture and affected Server/Python replay conformance using installed Python SDK 2.3.6 and the same published Server image. Keep #84 open until the published package proves the outcome.

No protocol contract changes. Server, PHP SDK, Rust SDK, CLI and Waterline do not embed the Python package and need no rebuild. Python documentation deploys from this repository after merge.