Fix documentation build warnings and errors

[antonwolfy]

The documentation build on master was completing with 2 errors and 123 warnings (see failing-ish run).
Although the job did not fail (Sphinx is not run with -W), several of these were silently degrading the published docs — dropping content and leaving empty API entries.

This PR fixes the Python-facing documentation defects. The build now completes with 0 errors and 108 warnings (the remaining 108 are pre-existing Doxygen/doxyrest C-API cross-reference noise in libsyclinterface, tracked separately).

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?
• If this PR is a work in progress, are you opening the PR as a draft?

[github-actions]

Deleted rendered PR docs from intelpython.github.com/dpctl, latest should be updated shortly. 🤞

[coveralls]

coverage: 74.579%. remained the same — fix-rendering-issues into master

[ndgrigorian]

LGTM

[ndgrigorian]

I'll note there are still 108 warnings but they seem to be from doxygen