Check `cargo rustdoc` for all workspace members

Currently `cargo doc --workspace --no-deps` throws warnings for some of our workspace packages, for example due to redundant_explicit_links and broken_intra_doc_links. To prevent documentation errors from persisting consider adding a CI job to check building the docs for each package. ### Tasks - [ ] Add `ci/check-docs.sh` script that runs `cargo rustdoc` for each package in the workspace. The script should fail if any cargo rustdoc invocations produce warnings - [ ] Add a `check-docs` job to `cont_integration.yml` that calls the check-docs.sh script - [ ] Add a justfile recipe `just doc` that similarly executes check-docs.sh Alternatively, use a 1-liner somewhere in `cont_integration.yml` (e.g. in build-test) such as RUSTDOCFLAGS='-D warnings' cargo doc --workspace --no-deps however that's not as explicit as it could be with respect to the crate names. **Build environment** - BDK tag/commit: fb05873a - OS+version: <!-- e.g. ubuntu 20.04.01, macOS 12.0.1, windows --> - Rust/Cargo version: 1.93.1 - Rust/Cargo target: <!-- e.g. x86_64-apple-darwin, x86_64-unknown-linux-gnu, etc. --> **Which backend(s) are relevant (if any)?** - [ ] Electrum - [ ] Esplora - [ ] Bitcoin Core RPC - [x] None / not backend-related (e.g. `bdk_chain`, `bdk_core`) - [ ] Other (please specify): `____` **Is this blocking production use?** - [ ] Yes - [x] No