fix(jwk): handle KeySet equality with unrelated types

[janmrow]

KeySet.__eq__ currently raises an exception when a KeySet is compared with an unrelated type.

This PR returns NotImplemented for unsupported types. This lets Python handle the comparison, while keeping existing KeySet-to-KeySet comparisons unchanged.

Regression tests cover comparisons with unrelated types, also including reflected equality.

Tests on local:

• pytest tests/ -q
• mypy src/joserfc/_keys.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.86%. Comparing base (397e04f) to head (8cf48fd).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #106   +/-   ##
=======================================
  Coverage   99.86%   99.86%           
=======================================
  Files          47       47           
  Lines        2955     2956    +1     
  Branches      352      353    +1     
=======================================
+ Hits         2951     2952    +1     
  Misses          2        2           
  Partials        2        2           

Flag	Coverage Δ
unittests	99.86% <100.00%> (+<0.01%)	⬆️

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