refactor(repo): layout crates into ./lib, ./bin, ./sdk

[Autoparallel]

Instead of having:

./crates/learner
./crates/learnerd
./crates/sdk

we could consider the above layout.

Furthermore

• Add a repo label to labels.yaml

One may also argue it may be better to also have: learnerd become learner-bin. I can look into crate renaming on crates.io, but I don't think we need to push on this latter part.