feat: cache cargo registry and target dirs keyed on Cargo.lock

.forgejo/workflows/macos.yml

@@ -21,6 +21,14 @@ jobs:
           repository: randogoth/fumi
           ref: main
           path: fumi
+      - uses: https://code.forgejo.org/actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            carrier/target
+            fumi/target
+          key: cargo-${{ hashFiles('carrier/Cargo.lock') }}
+          restore-keys: cargo-
       # Forgejo auto-injects GITHUB_TOKEN (GH Actions compatibility), scoped
       # to this Forgejo instance. Nix auto-detects that env var and assumes
       # it's a github.com credential, so it sends it to api.github.com when