Confusing exception name: WarningError

In https://github.com/DiamondLightSource/mx-bluesky/issues/1385, exceptions such as `WarningException` were renamed to `WarningError` to comply with pep8 naming conventions, where all exceptions should end in `Error`. This is confusing as this type of exception, and any that inherit from it, do not cause the program to crash, but for the pin to be skipped. Having something called `WarningError` is confusing and should be changed.

An option would be to use the [warnings module](https://docs.python.org/3/library/warnings.html#module-warnings) and avoid inheriting from `Exception`, which would relax the naming rule.

## Acceptance Criteria
- `WarningError` and its children are renamed to something sensible
- pep8 conventions are adhered to