[Clock] Review Test Cases and Discuss Structure and Objectives of Exercise

[BethanyG]

Filing this as a tracking issue and invitation to a discussion on revisions to this exercise.

The intent of Clock was to practice class customization and operator overloading via dunder methods in Python.
We've recently had quite a few changes, adding __repr__ to the mix, as well as additional instructions and tests in support of that change. A few issues have now come up around it:

1. Issue [Clock] Proposal for additional tests #2926
2. Issue [Clock] Improved/additional tests for __add__ and __sub__ #3008

It feels like this exercise is overloaded. It especially has too many tests, and is perhaps not clear enough in its directions and hints as to what the student does or does not need to think about for their implementations.

Thoughts on rework/adjustment clarification strategies welcome here.

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