docs: auto-add docstrings from MMCore.cpp

[tlambert03]

this PR adds a new command just add-docs, backed by scripts/add_docstrings.py that:

1. Uses Doxygen to parse C++ source files and output structured XML containing all documentation
2. Parses the Doxygen XML to create a mapping of ClassName::MethodName to docstring content
3. Scans the nanobind C++ file for .def() calls and adds missing docstrings
4. The updated bindings automatically propagate docstrings to the generated .pyi type stubs

I must be manually run, since i'm not 100% certain that it will always work... (uses some rather manual regexes). But it seems to be working well at the moment and definitely saves a lot of time in any case, leaving it only up to the reviewer to double check.

[codecov]

Codecov Report

Attention: Patch coverage is 89.35185% with 23 lines in your changes missing coverage. Please review.

Project coverage is 31.53%. Comparing base (9b9cd81) to head (47bf149).

Files with missing lines	Patch %	Lines
src/_pymmcore_nano.cc	89.35%	0 Missing and 23 partials ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             main      #59     +/-   ##
=========================================
  Coverage   31.53%   31.53%             
=========================================
  Files         138      138             
  Lines       18211    18211             
  Branches     7857     7857             
=========================================
  Hits         5743     5743             
+ Misses      10480     8450   -2030     
- Partials     1988     4018   +2030     

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