ci: move clippy to parallel job, off the build-linux critical path (#1000)

Extract full-workspace clippy into a standalone `clippy` job that runs
in parallel with build-linux. The new job excludes notebook, runtimed-wasm,
and runtimed-py (same pattern as rust-tests and windows-clippy).

Replace the full-workspace clippy in build-linux with a notebook-only
`cargo clippy -p notebook` which is fast since release deps are already
compiled. No clippy coverage is lost.

This removes ~2.5 minutes from the build-linux critical path.

Author: rgbkrk

.github/workflows/build.yml

@@ -263,8 +263,8 @@ jobs:
             cp target/release/runt "crates/notebook/binaries/runt-$TARGET"
           fi
 
-      - name: Clippy
-        run: cargo clippy --workspace --all-targets -- -D warnings
+      - name: Clippy (notebook crate)
+        run: cargo clippy -p notebook --all-targets -- -D warnings
 
       - name: Install cargo-binstall
         run: curl -L --proto '=https' --tlsv1.2 -sSf https://raw.githubusercontent.com/cargo-bins/cargo-binstall/main/install-from-binstall-release.sh | bash
@@ -336,6 +336,32 @@ jobs:
         # Exclude runtimed-py — requires Python/maturin (tested in runtimed-py-integration job).
         run: cargo test --workspace --exclude notebook --exclude runtimed-wasm --exclude runtimed-py --verbose
 
+  clippy:
+    name: Clippy (Linux)
+    needs: [changes]
+    if: needs.changes.outputs.source_changed == 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libgtk-3-dev libwebkit2gtk-4.1-dev libxdo-dev
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v7
+
+      - name: Install rust
+        uses: dsherret/rust-toolchain-file@v1
+
+      - uses: Swatinem/rust-cache@v2
+        with:
+          shared-key: ubuntu-latest
+
+      - name: Clippy
+        run: cargo clippy --workspace --exclude notebook --exclude runtimed-wasm --exclude runtimed-py --all-targets -- -D warnings
+
   build:
     name: ${{ matrix.platform.name }}
     needs: [changes, build-ui]