feat: build directory setting & reuse

[henryiii]

Support for custom build directory, opt-in. Using FORCE for the moment. Doesn't try to rewrite the paths for moving CMake yet, but the info for this is there in the new json file.

Maybe this shouldn't have a cmake. prefix? Edit: yes, looks like we could sync-up with meson-python if we just use build-dir, so let's go with that. See mesonbuild/meson-python#275 for builddir -> build-dir there.

• TODO: this should be able to (maybe via substitution?) have a unique path per interpreter.

Might adjust this later. My thought is we can make this opt-in for now, then if we make it opt-out, we can protect the change on a minimum version selection.

[codecov]

Codecov Report

Merging #181 (9479c50) into main (10f9a59) will decrease coverage by 0.25%.
The diff coverage is 73.07%.

@@            Coverage Diff             @@
##             main     #181      +/-   ##
==========================================
- Coverage   89.43%   89.18%   -0.25%     
==========================================
  Files          44       44              
  Lines        1865     1887      +22     
==========================================
+ Hits         1668     1683      +15     
- Misses        197      204       +7     

Impacted Files	Coverage Δ
src/scikit_build_core/builder/builder.py	95.45% <ø> (ø)
src/scikit_build_core/cmake.py	82.26% <69.56%> (-2.86%)	⬇️
src/scikit_build_core/build/wheel.py	91.30% <100.00%> (+0.07%)	⬆️
src/scikit_build_core/settings/skbuild_model.py	100.00% <100.00%> (ø)

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[henryiii]

This still doesn't provide any benefit, since the Python directories change between invocations. We could either sed one for the other, or we could declare that only non-isolated builds can benefit (at least the changing paths isn't breaking anything).

Edit: There was a mistake. Now provides full benefit for non-isolated builds. Isolated builds get partial benefit (things like moving source files via pybind11 still cause rebuilds AFAICT).