Greatly improve test coverage and make those tests pass

Unfortunately mixed with a lot of reformatting from fourmolu because the pre-commit hook really wants to do that now and I was not sufficiently vigilant to stop it every time...

But the main point of this is that it brings in test vectors from Tahoe-LAFS and then makes the encoder produce identical capabilities for all those cases.

Since the capabilities include hashes of almost all of the content of the shares, this demonstrates that the shares are also identical (probably! there might be some bookkeeping that doesn't get covered by hashes - TBD).