Add Python 3.15 support across all SDKs

[Bernd Verst (berndverst)]

Summary

• Declare Python 3.15 support in package classifiers for durabletask, durabletask.azuremanaged, and azure-functions-durable.
• Add Python 3.15 to all three SDK CI test matrices and their matching Nox sessions, preserving existing 3.13 and 3.14 test coverage.
• Move the standalone core and Azure Managed lint jobs from Python 3.14 to Python 3.15.
• Preserve Python 3.10 support for core/Azure Managed and the Functions SDK's Python 3.13 minimum. Minimum-version type checks and Functions host tests remain unchanged.
• Update development documentation and all three Unreleased changelogs. Package versions and dependency minimums are unchanged.

Validation

Unit tests passed on stable Python 3.15.0:

SDK	Passed
Core	1,109
Azure Managed	187
Azure Functions Durable	373

• Verified package metadata, unchanged minimum Python versions, and CI/Nox version parity.
• Flake8 checks passed for all package source and test directories and noxfile.py.
• Markdown lint passed for the updated development guide; changelog entries were reviewed manually.
• Host/emulator integration tests were not run locally. The updated CI matrices include Python 3.15 coverage.
• Pyright still reports the existing, unchanged optional-member-access diagnostic at noxfile.py:392 (session.run(...).strip()); this PR introduces no new diagnostic there.

[Copilot]

🟢 Approval recommended

The metadata, Nox sessions, CI matrices, documentation, and changelogs consistently add Python 3.15 without changing minimum-version contracts.

0 open findings

What changed in this PR

Adds Python 3.15 support across all three SDK packages while retaining existing minimum versions.

Changes:

• Adds Python 3.15 package classifiers and changelog entries.
• Extends Nox and CI test matrices through Python 3.15.
• Updates development guidance and moves core/Azure Managed linting to Python 3.15.

File	Description
pyproject.toml	Declares core SDK support through Python 3.15.
noxfile.py	Adds Python 3.15 test sessions.
durabletask-azuremanaged/​pyproject.toml	Declares Azure Managed support through Python 3.15.
durabletask-azuremanaged/​CHANGELOG.md	Records Python 3.15 support.
docs/​development.md	Documents updated Nox version coverage.
CHANGELOG.md	Records core SDK Python 3.15 support.
azure-functions-durable/​pyproject.toml	Declares Functions SDK support through Python 3.15.
azure-functions-durable/​CHANGELOG.md	Records Functions SDK Python 3.15 support.
.github/​workflows/​durabletask.yml	Tests core across Python 3.10–3.15.
.github/​workflows/​durabletask-azuremanaged.yml	Tests Azure Managed across Python 3.10–3.15.
.github/​workflows/​durabletask-azurefunctions.yml	Tests Functions across Python 3.13–3.15.

🧠 Review effort: Balanced

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