This PR is part of the issue #3492.
# Objective
- Add and update the bevy_tasks documentation to achieve a 100% documentation coverage (sans `prelude` module)
- Add the #![warn(missing_docs)] lint to keep the documentation coverage for the future.
## Solution
- Add and update the bevy_math documentation.
- Add the #![warn(missing_docs)] lint.
- Added doctest wherever there should be in the missing docs.