Improve types through typing all tests

[jodal]

• Upgrade pyright to 1.1.313
• Name type vars consistently
• Make ActorRef and ActorProxy generic
• Change the return type of ActorProxy.__getattr__() to Any
• Fully type test suite

[codecov]

Codecov Report

Patch coverage: 94.73% and project coverage change: +0.14 🎉

Comparison is base (952b5ea) 90.57% compared to head (ace6232) 90.72%.

❗ Current head ace6232 differs from pull request most recent head 3d92e9c. Consider uploading reports for the commit 3d92e9c to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #195      +/-   ##
==========================================
+ Coverage   90.57%   90.72%   +0.14%     
==========================================
  Files          12       12              
  Lines         573      582       +9     
==========================================
+ Hits          519      528       +9     
  Misses         54       54              

Impacted Files	Coverage Δ
src/pykka/_ref.py	88.15% <71.42%> (+0.15%)	⬆️
src/pykka/_actor.py	91.66% <100.00%> (+0.23%)	⬆️
src/pykka/_future.py	96.42% <100.00%> (+0.13%)	⬆️
src/pykka/_proxy.py	97.39% <100.00%> (+0.02%)	⬆️
src/pykka/_registry.py	94.28% <100.00%> (+0.08%)	⬆️
src/pykka/_threading.py	91.80% <100.00%> (ø)

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