Add more typeclass examples and test cases.

[micsza]

There is quite a lot of type-class (aka TC) examples and their derivations in tests but how about adding few more? This could be a good warm-up for new-coming contributors as well as it could provide the users more documentary examples of how to use magnolia api to create their own derivations.

Walk-through for newcommers:
0. Choose your base branch (scala2 vs scala3).

1. Browse through the existing TC examples, their derivations and test cases.
2. Invent your own fancy TC and write its derivation.
3. Add test cases using your TC.
4. Optionally, repeat for the other branch.

TCs improving the existing api usage documentation and tests for non-covered cases would be appreciated.