Add GitHub Actions workflow for Rust tests

Adds three CI jobs:
- rust-tests: Pure Rust workspace tests on Linux, macOS, Windows
- rust-ffi-tests: C++ test suite running against Rust FFI on Linux, macOS
- rust-lint: Clippy and rustfmt checks

Author: LegNeato

.github/workflows/rust.yml

@@ -0,0 +1,140 @@
+name: Rust
+
+permissions:
+  contents: read
+
+on:
+  push:
+    branches:
+      - 'main'
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  # Pure Rust tests
+  rust-tests:
+    name: Rust Tests
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: '0'
+
+      - name: Download SPIRV-Headers
+        run: python3 utils/git-sync-deps
+
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache Cargo
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            rust/target/
+          key: ${{ runner.os }}-cargo-${{ hashFiles('rust/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
+      - name: Build Rust workspace
+        working-directory: rust
+        run: cargo build --workspace
+
+      - name: Run Rust tests
+        working-directory: rust
+        run: cargo test --workspace
+
+  # Rust FFI pretending to be C++ - runs C++ test suite against Rust implementation
+  rust-ffi-tests:
+    name: Rust FFI (C++ Test Suite)
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: '0'
+
+      - name: Download dependencies
+        run: python3 utils/git-sync-deps
+
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache Cargo
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            rust/target/
+          key: ${{ runner.os }}-cargo-ffi-${{ hashFiles('rust/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-ffi-
+
+      - name: Configure CMake
+        run: |
+          cmake -B build \
+            -DSPIRV_BUILD_FUZZER=OFF \
+            -DSPIRV_USE_RUST_FFI=ON \
+            -DCMAKE_BUILD_TYPE=Release
+
+      - name: Build C++ with Rust FFI
+        run: cmake --build build --config Release -j $(nproc 2>/dev/null || sysctl -n hw.ncpu)
+
+      - name: Run C++ tests (backed by Rust)
+        working-directory: build
+        run: ctest --output-on-failure -j $(nproc 2>/dev/null || sysctl -n hw.ncpu)
+
+  # Clippy and format checks
+  rust-lint:
+    name: Rust Lint
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: '0'
+
+      - name: Download SPIRV-Headers
+        run: python3 utils/git-sync-deps
+
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy, rustfmt
+
+      - name: Cache Cargo
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            rust/target/
+          key: ${{ runner.os }}-cargo-lint-${{ hashFiles('rust/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-lint-
+
+      - name: Check formatting
+        working-directory: rust
+        run: cargo fmt --all -- --check
+
+      - name: Run Clippy
+        working-directory: rust
+        run: cargo clippy --workspace --all-targets -- -D warnings