Drop Python 3.9 support

[jhamon]

Summary

Removes support for Python 3.9, which has reached end-of-life, and updates all configuration and documentation to reflect Python 3.10+ as the minimum supported version. This simplifies dependency constraints and aligns with current Python support lifecycle.

Changes

Configuration Updates

• Updated pyproject.toml:
  • Changed requires-python from ">=3.9" to ">=3.10"
  • Removed "Programming Language :: Python :: 3.9" trove classifier
  • Updated Ruff target-version from "py39" to "py310"
  • Updated Black target-version from ["py39"] to ["py310"]
  • Simplified dependency constraints by removing Python 3.9-specific conditions:
    • pandas-stubs: Removed Python 3.8-3.9 fallback, now uses single version constraint
    • numpy: Removed Python 3.8-3.9 fallback, now uses single version constraint
    • pytest-benchmark: Simplified condition from python_version>='3.9' and python_version<'4.0' to python_version<'4.0'
    • sphinx: Simplified condition from python_version>='3.9' and python_version<'3.11' to python_version<'3.11'
    • myst-parser: Removed Python 3.9-3.10 fallback, now uses single version constraint
    • grpcio: Simplified condition from python_version>='3.8' and python_version<'3.11' to python_version<'3.11'
    • pandas: Simplified condition from python_version>='3.9' and python_version<'3.13' to python_version<'3.13'

Documentation Updates

• Updated README.md: Changed prerequisites from "Python 3.9 and greater" to "Python 3.10 and greater", and updated tested versions from "3.9 to 3.13" to "3.10 to 3.13"
• Updated docs/index.rst: Changed prerequisites from "Python 3.9 and greater" to "Python 3.10 and greater", and updated tested versions from "3.9 to 3.13" to "3.10 to 3.13"
• Updated docs/upgrading.md: Added breaking change note in the 7.x section documenting the removal of Python 3.9 support

Breaking Changes

⚠️ Python 3.9 is no longer supported. Users must upgrade to Python 3.10 or later to use this version of the SDK.

Impact

• Users on Python 3.9: Must upgrade to Python 3.10+ to continue using the SDK
• Dependency resolution: Simplified constraints may allow newer package versions to be installed
• CI/CD: No changes needed as workflows already use parameterized Python versions (3.10, 3.11, 3.12, 3.13)

Rationale

Python 3.9 reached end-of-life on October 2, 2025. Dropping support allows us to:

• Simplify dependency management by removing version-specific constraints
• Take advantage of Python 3.10+ features and improvements
• Reduce maintenance burden by focusing on actively supported Python versions
• Align with the Python community's support lifecycle

Files Changed

• pyproject.toml
• README.md
• docs/index.rst
• docs/upgrading.md