Update CVSClient for run_process(), type safety, and deprecations.
Update CVSClient for run_process(), type safety, and deprecations.

`CVSClient` now uses `run_process()` instead of `execute()` for all
`cvs` interaction, giving us better type safety and safer execution.

All methods have been updated with type annotations, ensuring compliance
with `BaseSCMClient` requirements. Documentation has been updated where
appropriate.

Some deprecated calls have been updated, and dead code removed.

Testing Done:
Unit tests pass on Python 3.7-3.11.

Reviewed at https://reviews.reviewboard.org/r/12570/

reviewboard/rbtools,reviewboard/rbtools,reviewboard/rbtools