Add more test coverage for Tsavorite primitives

[PaulusParssinen]

Add more SpanByte and its associated logic unit test coverage. Also contains some Tsavorite test code housekeeping.

TODO

• More SpanByte specific unit tests to Tsavorite.test

[badrishc]

This may still be needed, as the MetadataSize check is different from Length check. A SpanByte may have an 8 byte optional header used for storing logical record expiration time (a bit tells us whether there is such a header). The MetadataSize check ensures that both left and right have such a metadata header. MetadataSize will be either 8 or 0, depending on this bit.

[PaulusParssinen]

Ah, thanks for explanation. I should have looked where that getter leads to before jumping to conclusion. 🤦‍♂️

I probably should pivot this PR to add tests to catch this detail, that the KeyComparer must be able to distinguish SpanBytes if their MetadataSizes are different. Bit spooky that the CI passed