mypy: Enable --warn-unused-ignores and remove unused ignores

[bkeryan]

• This contribution adheres to CONTRIBUTING.md.
• I've updated CHANGELOG.md if applicable.
• I've added tests applicable for this pull request

What does this Pull Request accomplish?

Configure mypy to --warn-unused-ignores, except for mypy-protobuf codegen.

Remove unused ignores:

• ctypes callback function with no arguments no longer warns.
• Properties can now have different get/set types, as of Mypy 1.16: https://mypy-lang.blogspot.com/2025/05/mypy-116-released.html
• ZoneInfo constructor type: ignore is no longer needed. This might have been for Python 3.8 timezone backports?
• Watchdog expiration states do not have enough type hints to generate the expected warnings.

Why should this Pull Request be merged?

Closes #613

What testing has been done?

Ran mypy.

[github-actions]

Test Results

    34 files  ±0      34 suites  ±0   56m 57s ⏱️ -26s
 2 461 tests ±0   2 091 ✅ ±0    370 💤 ±0  0 ❌ ±0 
43 920 runs  ±0  37 508 ✅ ±0  6 412 💤 ±0  0 ❌ ±0 

Results for commit de62f2c. ± Comparison against base commit f10feb9.

♻️ This comment has been updated with latest results.