Clean up namespaces - part 1 (backport #637)

[mergify]

Splitting the work created from @mjcarroll in #502. This is smaller to make sure it's correct. I'll make the next PRs a bit bigger.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

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This is an automatic backport of pull request #637 done by Mergify.