Add rust-cache composite action

.gitea/actions/rust-cache/action.yml

@@ -0,0 +1,48 @@
+name: Rust Setup + Cache
+description: Install Rust toolchain and cache cargo/rustup dependencies for Gitea Actions
+author: eric
+
+inputs:
+  toolchain:
+    description: Rust toolchain to install (e.g., stable, 1.75.0, nightly)
+    default: stable
+    required: false
+
+outputs:
+  cache-hit:
+    description: "Whether a cache entry was found"
+    value: ${{ steps.cache.outputs.cache-hit }}
+
+runs:
+  using: composite
+  steps:
+    - name: Cache cargo + rustup
+      id: cache
+      uses: https://gitea.com/actions/cache@v3
+      with:
+        path: |
+          ~/.cargo/registry
+          ~/.cargo/git
+          ~/.rustup/toolchains
+          ~/.rustup/settings.toml
+          target
+        key: rust-linux-${{ hashFiles('**/Cargo.lock') }}-${{ hashFiles('**/Cargo.toml') }}
+        restore-keys: |
+          rust-linux-${{ hashFiles('**/Cargo.lock') }}-
+          rust-linux-
+
+    - name: Setup Rust
+      shell: bash
+      run: |
+        # If toolchain was cached, rustup will skip download — install still runs for metadata
+        curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs \
+          | sh -s -- -y --default-toolchain ${{ inputs.toolchain }}
+        # Add cargo bin to PATH for subsequent steps
+        echo "$HOME/.cargo/bin" >> $GITHUB_PATH
+
+    - name: Show cached sizes
+      shell: bash
+      run: |
+        echo "=== ~/.cargo ===" && du -sh ~/.cargo 2>/dev/null || echo "(empty)"
+        echo "=== ~/.rustup ===" && du -sh ~/.rustup 2>/dev/null || echo "(empty)"
+        echo "=== target ==="   && du -sh target 2>/dev/null   || echo "(empty)"