adds nanobind scaffolding for future python bindinds

[antond-weta]

This adds all necessary code to start working on python bindings.

• configures nanobind
• adds a target rawtoaces_bindings
• adds some minimal bindings for testing purposes

Note, I've only added minimal bindings necessary to convert an image. The stuff I've implemented:

• ImageConverter.process_image() - an example of bindings for a class and a method. It is working, and is enough to get an image converted with the default settings
• ImageConverter.settings.WB_method - an example of bindings of a nested class and an enum.

I have made sure that the code builds on all platforms on CI, but I have only tested the python code on my machine (Mac).
Here is how I tested:

• go to the folder where the built bindings library is located, of add the path to PYTHON_PATH and/or DYLD_LIBRARY_PATH, this may be platform-dependent,
• execute this python code:

% python
>>> import rawtoaces
>>> converter = rawtoaces.ImageConverter()
>>> converter.process_image("/path/to/a/raw/file")

Next steps from here:

0. Set up python-based unit tests for future bindings. Ideally all bindings should have 100% test coverage.
1. Implement bindings for all properties and file-based methods from rta::util::ImageConverter, which do not use any OpenImageIO types as parameters or return values. The bindings in OIIO are currently implemented with pybind, but there is a plan to rewrite them with nanobind.
2. Implement bindings for rta::core::SpectralSolver and rta::core::MetadataSolver.
3. If the work to convert OIIO to nanobind hasn't been done yet, implement bindings for the OIIO::ImageBuf-based API by converting the ImageBufs to/from numpy arrays.
4. After OIIO has been converted to nanobind, finish up implementing the OIIO::ImageBuf-based API by exposing the OIIO types on the python side.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.27%. Comparing base (184bbc4) to head (c3b8e05).

Additional details and impacted files

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##             main     #205   +/-   ##
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  Coverage   72.27%   72.27%           
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  Files          10       10           
  Lines        2348     2348           
  Branches      311      311           
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  Hits         1697     1697           
  Misses        651      651           

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[soswow]

comments. needed?

[antond-weta]

I don't know. I think the binary should be versioned, but uncommenting that makes configure fail.

Also I don't know if this whole 'export' thing is needed, I use it to change the library name, as the 'rawtoaces' target name is already taken. This also makes the library install with the rest of targets, I don't know if the destination should be different. This is good enough for now. We'll need somebody more familiar with python tools deployment to finalise this, I suppose.

[lgritz]

I'm not sure this builds and installs the OIIO python bindings by default. You may need some kind of modifier.

[antond-weta]

Noted. Will check. We don't need OIIO on the python side that right now.