Deprecate Python 3.9 support

[Copilot]

Removes Python 3.9 from supported versions. Minimum required version is now Python 3.10.

Changes

• setup.py: Updated python_requires=">=3.10" and removed 3.9 classifier
• pyproject.toml: Removed py39 from Black target versions
• tox.ini:
  • Removed py39 from test environments
  • Updated min_versions, lint, and format testenvs to use python3.10 as basepython
  • Consolidated gh-actions mapping (3.10 now runs lint and check-packaging)
• .github/workflows/run-tox.yml: Removed 3.9 from CI matrix, use 3.10 for min_versions testing

Original prompt

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This section details on the original issue you should resolve

<issue_title>Deprecate python 3.9</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Deprecate python 3.9 #137

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