Refactor: Replace BitVec dependency with plain bool vectors

[jbeyerstedt]

The bitvec crate seems to be unmaintained and is not compatible with the latest Nom release (if we need to update at some point).

It also doesn't help us quite so much here since most of the data is byte aligned anyways, so I would rather have less dependencies and a bit more code.
I added a dependency on arbitrary-int though to properly represent the 4, 5 and 15 bit values we have.

TODO:

• Test with more data than in the unit tests
  • Encoding works just fine
• Wait to have a release version of 0.3.0 before merging these potentially breaking changes

[jbeyerstedt]

rebased to clean up merge conflicts (since main-branch has experienced some refactoring)

[jbeyerstedt]

Now all individual commits compile again

[BendixBuchheister]

I haven't looked into all the changes from each struct, and focussed more on looking at the new encode/decode functions.
That part looks fine to me, and since the unit tests still work, and you already tested that everything still works with real data, i would say the code should be fine to merge