simplify building and testing configs

[jameslamb]

This is exactly the same set of changes already approved in #69.

cugraph-docs was switched from private to public during the lifetime of that PR, which put CI into a state where that PR couldn't be merged: #69 (comment)

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Development and the vision for this project has stabilized here quite a bit over the last few weeks, so I think it's a good time to simplify things.

This proposes the following:

• removing configuration for codecov
  • (there are no tests running here)
• removing patterns in CODEOWNERS that don't match any files
• removing anything related to CUDA 11, pyproject.toml, or requirements.txt in dependencies.yaml and related files
  • this repo exclusively uses conda, and only a single major version of CUDA
• updating to sphinx>=8 and breathe>=4.35
  • to match the rest of RAPIDS, e.g. Remove sphinx pinning cugraph#4839, Use nvidia-sphinx-theme for docs cuvs#528
  • floors also mean faster conda solves and fewer surprises at build time
• removing unnecessary files in ci/utils
  • these appear to have been copied from cugraph, but they're not needed as we don't do notebook testing here

Notes for Reviewers

How I tested this

Tested the update-version.sh changes like this:

./ci/release/update-version.sh '25.04.00'

git grep -E '25\.2'
git grep -E '25\.02'

[acostadon]

Looks great

[jameslamb]

/merge