Upcoming Deprecation: Python 3.9 Support

[ianna]

Support for Python 3.9 in Awkward Array is planned to be deprecated in a future release.
As Python 3.9 has reached end-of-life, we encourage users to begin migrating to Python 3.10 or newer to ensure continued compatibility, access to new features, and ongoing security updates.

We will provide advance notice before the deprecation becomes effective.
If you have feedback or concerns regarding this transition, please open an issue on the Awkward Array GitHub repository.