Miscellaneous improvements throughout the codebase

[trag1c]

Joint PR w/ @bswck :)

[bswck]

Summary:

• Improved performance:
  • Optimized some calculations.
  • Introduced variables for objects that were suboptimally recreated instead of being reused.
  • Replaced == with is where applicable.
• Used good practices:
  • Removed unnecessary () when raising exceptions without arguments.
  • Used pathlib instead of os.path where possible.
  • Used a list comprehension instead of a for+list.append() loop.
  • Reduced code repetition (where the repetition was unnecessary).
  • Replaced dict.keys() with dict when iterating over dictionary keys.
  • Used contextlib.suppress() in a try-except-pass scenario.
  • Used builder pattern to improve readability.
  • Replaced most one-use variables with drop-in expressions.
  • Replaced str.find(x) == 0 with str.startswith(x) and str.find(x) == -1 with x not in str.
  • Replaced return None with return in functions whose return value is None.
  • Used positive logic checking in conditional expressions/statements where it increases legibility.
• Introduced naming changes in local variables—changing parameter names was avoided not to introduce breaking changes:
  • Corrected some names not to shadow identifiers from the built-in scope.
  • Made one-letter variable names in gen/list/dict comprehensions more verbose and meaningful.
• Improved type hinting:
  • Corrected some type annotations to reflect the runtime reality.
  • Added some missing type annotations, shortened Literal[k] | Literal[j] to Literal[k, j].
• Replaced X.__class__ with type(X) (there is no need to respect the descriptor behavior of __class__ for Event objects, can they ever be weakref proxies?).
• Applied De Morgan's laws in conditional statements where applicable.
• Corrected some docstrings to start with imperative mood.

[Secrus]

Great work overall!