Remove unused typing_extensions dependency

[jwodder]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.88%. Comparing base (245b97f) to head (124f077).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #10      +/-   ##
==========================================
+ Coverage   96.06%   96.88%   +0.81%     
==========================================
  Files           3        3              
  Lines         229      225       -4     
  Branches       38       37       -1     
==========================================
- Hits          220      218       -2     
+ Misses          4        3       -1     
+ Partials        5        4       -1     

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