docs: Add composefs-rs crates to internals rustdoc

[cgwalters]

These external git dependencies don't have docs on docs.rs, so include them in the internal documentation alongside our workspace crates.

Assisted-by: OpenCode (Opus 4.5)

[gemini-code-assist]

Code Review

This pull request updates the documentation build process to include rustdoc for the external composefs-rs git dependencies. The changes modify docs/Dockerfile.mdbook to generate the documentation and docs/src/internals.md to add links to it. This is a good addition as it makes documentation for these key dependencies available locally. The implementation is correct, but I have one suggestion to ensure the generated documentation for the external crates is as comprehensive as for the internal ones.

[jeckersb]

LGTM, sanity checked locally. Not sure why the docs job is failing in CI, it works fine for me locally and it's all done in the container build so I don't see why it would be any different in CI...

[cgwalters]

It's because

INFO has_release_artifact{release=GhRelease { repo: GhRepo { owner: "cargo-bins", repo: "cargo-quickinstall" }, tag: "mdbook-linkcheck-0.7.7" } artifact_name="mdbook-linkcheck-0.7.7-x86_64-unknown-linux-gnu.tar.gz"}:do_send_request{request=Request { method: GET, url: Url { scheme: "https", cannot_be_a_base: false, username: "", password: None, host: Some(Domain("api.github.com")), port: None, path: "/repos/cargo-bins/cargo-quickinstall/releases/tags/mdbook-linkcheck-0.7.7", query: None, fragment: None }, headers: {"accept": "application/vnd.github+json", "x-github-api-version": "2022-11-28"} } url=https://api.github.com/repos/cargo-bins/cargo-quickinstall/releases/tags/mdbook-linkcheck-0.7.7}: Received status code 403 Forbidden, will wait for 120s and retry

So cargo-binstall falls back to building from source which for bad reasons also includes building openssl from source which for historical reasons requires Perl stuff we don't ship in the devenv.

[cgwalters]

I tried adding a commit here to propagate the github token into the podman build, which I think will mean that cargo-binstall provides it when doing fetches which should avoid having us be ratelimited as if we were doing anonymous requests.

[jeckersb]

Oops forgot I have to re-review now 😆