ci: add GitHub Actions CI and release workflows

Add ci.yml running fmt, clippy, build, and test on stable + nightly
Rust for PRs and pushes to main. Add release.yml for automated crate
publishing to crates.io on version tag pushes. Remove dead_code allow
and add crate-level doc comment with usage example.

.github/workflows/release.yml

@@ -0,0 +1,39 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - "v*.*.*"
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  publish:
+    name: Publish to crates.io
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust stable
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache cargo registry and build
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-release-${{ hashFiles('**/Cargo.toml') }}
+
+      - name: Build release
+        run: cargo build --release
+
+      - name: Run tests
+        run: cargo test
+
+      - name: Publish to crates.io
+        run: cargo publish
+        env:
+          CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }}