End Python 3.9 support

[d33bs]

Description

This PR ends Python 3.9 support within this project (Python 3.9 is end of life as of October 2025).

What is the nature of your change?

• Bug fix (fixes an issue).
• Enhancement (adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• This change requires a documentation update.

Checklist

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[gwaybio]

Maybe this is overthinking, but should we think about release schedules for this depreciation? In other words, should we bundle this in the current change set or release prior to merging this?

[d33bs]

Thanks @gwaybio, releasing, and then merging this after sounds like a good plan to me!