Unserialize reprlocals to a ReprLocal instance

[timyhou]

This is in reference to issue #176 and a continuation of PR #164 and #171

I had to instantiate ReprLocals. Added more asserts around comparing the initial report against the result after being serialized, unserialized.

I think in the initial review @RonnyPfannschmidt mentioned this kind of functionality should me moved in pytest-core. I wholeheartedly agree, since I am terrible at handling it myself. Please be critical of my method since I obviously keep overlooking aspects and introducing new issues.

Thanks for submitting a PR, your contribution is really appreciated!

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[RonnyPfannschmidt]

@timyhou dont feel down, you are introducing a entirely new feature level and its not easy to do so

your quick handling of the problem as they come up is exemplary and noteworthy 👍
after all the problem is something that has no tests to show for to begin with since it wasn't even halfway possible before

when you explore new horizons there are minor setbacks to be expected, and you navigates those well

[timyhou]

Thanks for the words of encouragement!

The test failure is TestDistribution.test_keyboard_interrupt_dist _ which also occurred during #170 so I will assume the judgement is the same?

not trivial to fix but also not critical

[RonnyPfannschmidt]

yup, that failure is unrelated, things look good
i think its fine to merge after @nicoddemus had a look

[nicoddemus]

Thanks @timyhou!