Update type hints

[AdeelH]

Overview

This PR updates type hints and improves docstrings.

Changes include:

• Replace deprecated aliases: Callable, Dict, List, Set, Tuple, Type, with the recommended replacements
• Replace Optional[x] with x | None
• Replace Union[x, y, ...] with x | y | ...
• Add signature to Callable type hints where feasible
• Use Self where applicable
• Remove argument type hints from docstrings (non-exhaustive)
• Fix/improve docstrings

Checklist

• [x] Added unit tests, if applicable
• [ ] Updated documentation, if applicable
• [ ] Added needs-backport label if the change should be back-ported to the previous release
• [x] PR has a name that won't get you publicly shamed for vagueness

Notes

N/A

Testing Instructions

N/A

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 99.45455% with 3 lines in your changes missing coverage. Please review.

Project coverage is 90.09%. Comparing base (8f9f6d4) to head (02c9ffd). Report is 40 commits behind head on master.

Files with missing lines	Patch %	Lines
...ervision_core/rastervision/core/data/utils/misc.py	80.00%	1 Missing :warning:
...vision/pytorch_learner/object_detection_learner.py	80.00%	1 Missing :warning:
...earner/rastervision/pytorch_learner/utils/utils.py	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2192 +/- ## ======================================= Coverage 90.08% 90.09% ======================================= Files 198 198 Lines 9877 9879 +2 ======================================= + Hits 8898 8900 +2 Misses 979 979 ```

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