Update sortedmap

[frmdstryr]

This slightly reworks the constructor to add support for tp_vectorcall (~30% faster construction of empty sortedmap when available) and addresses the recent code review items.

Edit: Also adds a special case for doing a sortedmap copy in the constructor.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.52%. Comparing base (d9454af) to head (07dad1b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #263   +/-   ##
=======================================
  Coverage   97.52%   97.52%           
=======================================
  Files          24       24           
  Lines        1093     1093           
  Branches      167      167           
=======================================
  Hits         1066     1066           
  Misses         13       13           
  Partials       14       14           

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