ferric-example: commit Cargo.lock to pin the Rust toolchain deps

CI resolved Rust dependencies fresh on every run because Cargo.lock was
gitignored (a leftover from the initial `cargo new --lib` scaffolding in
#43 — the stock library-crate convention). That let `napi-derive-backend`
float to 5.1.2, which expands the `#[napi]` attribute macro into a broken
`ctor` `unify_features` invocation ("expected `(`, found `]`"), failing the
bootstrap build of every CI job that compiles ferric-example.

ferric-example is a `crate-type = ["cdylib"]` that builds a final `.node`
artifact, not a library published to crates.io, so committing Cargo.lock is
the recommended practice — the direct analogue of package-lock.json. The
committed lock pins napi-derive-backend 5.0.2 (last known-good). Verified
with `cargo build --locked`.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: kraenhansen

packages/ferric-example/.gitignore

@@ -1,5 +1,4 @@
 /target
-Cargo.lock
 
 /*.xcframework/
 /*.apple.node/