fix(ci): install rustfmt component for the pinned toolchain

The old `rustup toolchain install stable` was a no-op because runners
preinstall stable with rustfmt included. The pinned 1.96.1 toolchain is
a fresh install under the runner's minimal rustup profile, which has no
rustfmt, so `cargo fmt --check` failed. Add it alongside
llvm-tools-preview in the test job's install step.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: BtXin

.github/workflows/ci.yml

@@ -159,8 +159,12 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y protobuf-compiler
       - name: Install Rust
-        # Version comes from rust-toolchain.toml.
-        run: rustup toolchain install --component llvm-tools-preview
+        # Version comes from rust-toolchain.toml. Components are listed here
+        # rather than in the toolchain file so the Docker build doesn't pull
+        # them: rustfmt for `cargo fmt`, llvm-tools-preview for coverage.
+        # Runners install fresh pinned toolchains with the minimal profile,
+        # which includes neither.
+        run: rustup toolchain install --component llvm-tools-preview,rustfmt
       - name: Install cargo-llvm-cov
         uses: taiki-e/install-action@cargo-llvm-cov
       - name: install nextest