chore(python): drop support for Python 3.9

[glevco]

Motivation

Remove support for Python 3.9 so we can use the new features and performance improvements from Python 3.10. Here are some of the main highlights:

• PEP 604 - Allow writing union types as X | Y
  • This is preferred than using Union and Optional
• PEP 612 - Parameter Specification Variables
  • Allows for named parameters in Callable definitions
• PEP 634, PEP 635, PEP 636 - Structural Pattern Matching
  • Great modern feature that eases functional-style programming

And the complete list: https://www.python.org/downloads/release/python-3100/

Acceptance Criteria

• Remove all mentions and uses of Python 3.9

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged