Refactor project for JOSS-ready packaging with CI, docs, and ReadMe

[bmusangu]

This PR modernizes the BlockInverseGPFA package to prepare it for community use, continuous integration, and publication. It includes major packaging, and documentation updates:

• Declared all core dependencies and optional extras:
  • [test]: for pytest-based testing
  • [docs]: for Sphinx documentation build
• Removed requirements.txt (no longer needed).
• Users can now install the package with:

 pip install .
 pip install .[test]
 pip install .[docs]
 
- Added `.readthedocs.yml` for Read the Docs builds
- Updated `ReadMe.md`

[jdrugo]

Changes look mostly good.

One issue is with the pyproject.toml license line, which should just specify the license through license = "BSD-3-Clause" rather than as file and text. This should fix the the failing tests.

Once the test run, the PR can be merged.