fix: stricter type hints for service decorators

[dlech]

Make strict type checkers happier by adding more precise type hints to the dbus_method, dbus_signal and dbus_property decorators.

Also improve internal type hints in the file while we're at it. This is mostly adding generic parameters to types that expect them.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.26%. Comparing base (9aa8f56) to head (71fed27).
⚠️ Report is 27 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #549   +/-   ##
=======================================
  Coverage   85.25%   85.26%           
=======================================
  Files          28       28           
  Lines        3431     3433    +2     
  Branches      601      601           
=======================================
+ Hits         2925     2927    +2     
  Misses        313      313           
  Partials      193      193           

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[codspeed-hq]

CodSpeed Performance Report

Merging #549 will not alter performance

_{Comparing decorator-type-hints (71fed27) with main (9aa8f56)}

Summary

✅ 6 untouched