Support python 3.14, unsupport python 3.9

[albertyw]

Python 3.14 is now released; add support and test against Python 3.14 in django-silk.

Python 3.9 support has ended; remove Python 3.9 from django-silk.

Ref: https://endoflife.date/python

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.33%. Comparing base (1b68320) to head (ef18638).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #834   +/-   ##
=======================================
  Coverage   87.33%   87.33%           
=======================================
  Files          53       53           
  Lines        2172     2172           
=======================================
  Hits         1897     1897           
  Misses        275      275           

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