Change _Shape to Shape and add comments for subclasses of Shape

Summary

Related to #1555
Change _Shape into Shape
- If a class is marked as private: When a class name starts with an underscore (_), it is considered a private class and may be ignored by automatic documentation tools. To resolve this, try renaming the class to make it public.
Add comments for subclasses of Shape

How to test

Checklist

[ ] I have added unit tests to cover my changes.
[ ] I have added integration tests to cover my changes.
[ ] I have added the description of my changes into CHANGELOG.
[X] I have updated the documentation accordingly

License

[ ] I submit my code changes under the same MIT License that covers the project. Feel free to contact the maintainers if that's a concern.
[ ] I have updated the license header for each file (see an example below).

# Copyright (C) 2024 Intel Corporation
#
# SPDX-License-Identifier: MIT

Codecov Report

Attention: Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.03%. Comparing base (9bdf8de) to head (91752eb). Report is 6 commits behind head on develop.

Files	Patch %	Lines
.../data_formats/datumaro_binary/mapper/annotation.py	66.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1568 +/- ## ======================================== Coverage 81.03% 81.03% ======================================== Files 276 276 Lines 32430 32430 Branches 6595 6595 ======================================== Hits 26280 26280 Misses 4696 4696 Partials 1454 1454 ``` | [Flag](https://app.codecov.io/gh/openvinotoolkit/datumaro/pull/1568/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openvinotoolkit) | Coverage Δ | | |---|---|---| | [ubuntu-20.04_Python-3.10](https://app.codecov.io/gh/openvinotoolkit/datumaro/pull/1568/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openvinotoolkit) | `81.02% <94.44%> (ø)` | | | [windows-2022_Python-3.10](https://app.codecov.io/gh/openvinotoolkit/datumaro/pull/1568/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openvinotoolkit) | `81.01% <94.44%> (ø)` | | 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=openvinotoolkit#carryforward-flags-in-the-pull-request-comment) to find out more.

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openvinotoolkit / datumaro