Migrate to nanobind and pyfans installation

[sanathkeshav]

• pyFANS becomes a standalone nanobind project built against an installed FANS.
• Ships as one abi3 wheel for Python 3.12+ with proper metadata.
• FANS_LIBRARY_FOR_MICRO_MANAGER is gone; build FANS, then pip install ./pyfans.
  Bindings now need Python 3.12+.

Architectural style adapted from #126 and therefore supersedes it.

Checklist:

• I made sure that the CI passed before I ask for a review.
• I added a summary of the changes (compared to the last release) in the CHANGELOG.md.
• If necessary, I made changes to the documentation and/or added new content.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[IshaanDesai]

Thanks a lot for this, it simplifies many things! I tested pyfans standalone, and it works as expected 👍 I would like to test a few features of the Micro Manager, but I won't be able to do it for the next few weeks, so I would suggest going ahead and merging this. The test_pyfans/README seems to be outdated now. As this PR further separates pyfans from FANS, we could consider making it a standalone package at some point.