(build): Need a config to ignore test data

[madhavmk]

• MANIFEST.in file is used only when using the setuptools build system. However as mentioned in the pyproject.toml we are using hatchling build system instead. We can therefore remove this MANIFEST file.
• Exclude the ./tests directory from the build step. the source distribution file reduced in size significantly. This speeds up gnatss pip installation speed due to faster downloading, and lesser unzipping.
• Solves Issue #220

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (73cbcac) 49.67% compared to head (470deee) 49.67%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #221 +/- ## ======================================= Coverage 49.67% 49.67% ======================================= Files 16 16 Lines 930 930 ======================================= Hits 462 462 Misses 468 468 ```

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[madhavmk]

The point of concern is the large size of the ./tests directory, which causes the gnatss source distribution tar file to be unnecessarily large. In the future we are likely to increase the ./tests directory size significantly by adding additional data files. `

[SSEC/offshore-geodesy]$ du -sh * 4.0K LICENSE 0 MANIFEST.in 12K README.md 844K docs 4.0K noxfile.py 4.0K pyproject.toml 140K src 15M tests

[SSEC/offshore-geodesy]$ python -m build ... [SSEC/offshore-geodesy]$ du -sh dist/* 44K dist/gnatss-0.1.dev106-py3-none-any.whl 4.7M dist/gnatss-0.1.dev106.tar.gz `

After excluding the ./tests directory from the build step, the source distribution file reduced in size significantly. This speeds up gnatss pip installation speed due to faster downloading, and lesser unzipping. `

[SSEC/offshore-geodesy]$ du -sh 4.0K LICENSE 0 MANIFEST.in 12K README.md 844K docs 4.0K noxfile.py 4.0K pyproject.toml 140K src 15M tests [SSEC/offshore-geodesy]$ python -m build ... [SSEC/offshore-geodesy]$ du -sh dist/ 44K dist/gnatss-0.1.dev107-py3-none-any.whl 788K dist/gnatss-0.1.dev107.tar.gz `