Add occlusion analysis to post-processing

[rwood-97]

Summary

This adds occlusion analysis code to MapReader's post-processing methods.

Fixes #466 Fixes #468

Describe your changes

This PR:

• Adds OcclusionAnalyzer class to MapReader post processing
• Renames PostProcessor to ContextPostProcessor
• Renames criterion to loss_fn

Checklist before assigning a reviewer (update as needed)

• [x] Self-review code
• [x] Ensure submission passes current tests
• [x] Add tests
• [x] Update relevant docs

Reviewer checklist

Please add anything you want reviewers to specifically focus/comment on.

• [ ] Everything looks ok?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.69737% with 7 lines in your changes missing coverage. Please review.

Project coverage is 63.35%. Comparing base (e459639) to head (014bb64). Report is 4 commits behind head on main.

Files	Patch %	Lines
mapreader/classify/classifier.py	72.22%	5 Missing :warning:
mapreader/__init__.py	90.00%	1 Missing :warning:
mapreader/process/occlusion_analysis.py	99.23%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #470 +/- ## ========================================== + Coverage 62.24% 63.35% +1.11% ========================================== Files 44 46 +2 Lines 7045 7292 +247 ========================================== + Hits 4385 4620 +235 - Misses 2660 2672 +12 ``` | [Flag](https://app.codecov.io/gh/Living-with-machines/MapReader/pull/470/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Living-with-machines) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/Living-with-machines/MapReader/pull/470/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Living-with-machines) | `63.35% <97.69%> (+1.11%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Living-with-machines#carryforward-flags-in-the-pull-request-comment) to find out more.

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