[#673] Add a way to clarify custom cleveland errors

Description

Problem: A function adding some prefix to CustomTestError text can be very useful for clarifying where the test fails.

Solution: add cmiThrow to rethrow arbitrary exceptions from MonadCleveland. Add clarifyErrors helper that wraps some action and adds a given prefix to CustomTestErrors that are generated by said action.

Related issue(s)

Resolves #673 (closed)

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