Simplify cmake cuda setup

[iiiian]

This PR streamlines the CMake CUDA setup by:

• Disabling CUDA builds by default.
• Set CUDA architecture to native if not specified. Avoid poking into the internal of Scalable CCD.
• Bump cmake minimum version to 3.24 to support CMAKE_CUDA_ARCHITECTURES="native"

Since cuda code is sensitive to environment changes (i.e. IPC fails to build on CUDA 13.0+), enabling it implicitly can create surprises for its consumer. As a library, CUDA build should be guarded behind a cmake option.

Also, ipc-toolkit currently inherits the cuda architecture from Scalable CCD, which defaults to "native" if not defined. Instead, we should handle this explicitly.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.40%. Comparing base (112712c) to head (3b82be6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #201   +/-   ##
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  Coverage   97.40%   97.40%           
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  Files         149      149           
  Lines       23748    23748           
  Branches      797      797           
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  Hits        23132    23132           
  Misses        616      616           

Flag	Coverage Δ
unittests	97.40% <ø> (ø)

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[zfergus]

Can you also add a note about CUDA support to the README.md and docs/source/build/c++.rst files?

[iiiian]

Now IPC will set CMAKE_CUDA_ARCHITECTURES to native if not specified. I also update READMD, build doc, and bump minimal cmake version to 3.24 across the repo. This should work in our CI/CD since Ubuntu 24.04 comes with cmake 3.28 by default.