Move out bindings

[clehner]

Like didkit-go and didkit-python, the other DIDKit language bindings/FFIs and their examples should be moved out into separate repos, which would each depend on the didkit Rust crate.

Moving out the bindings should help simplify this repo and improve CI build times. In particular, removing the "Build Android Archive" CI step would reduce the per-commit CI run time here by half (~30 minutes).

Possibly the C FFI can be kept in the didkit crate, since it is relied on in multiple places (Dart/Flutter, iOS/Swift, and Android/JNI). However, those should probably each depend on language-specific bindings for async support (#287) rather than using the blocking C functions.

Bindings to move out

• Android + JNI
• iOS/Swift
• Dart/Flutter
• WASM (Web + Node.js)
• Node.js (Neon)