Enable CI caching

.github/workflows/docs.yml

@@ -20,6 +20,7 @@ jobs:
           # Needed for use of unstable options
           toolchain: nightly
           override: true
+      - uses: Swatinem/rust-cache@v1
       - name: Build docs
         uses: actions-rs/cargo@v1
         env:

.github/workflows/msrv.yml

@@ -25,6 +25,12 @@ jobs:
           profile: minimal
           toolchain: stable
           override: true
+      - uses: Swatinem/rust-cache@v1
+        with:
+          # A stable compiler update should automatically not reuse old caches.
+          # Add the MSRV as a stable cache key too so bumping it also gets us a
+          # fresh cache.
+          sharedKey: msrv1.55
       - name: Run checks
         uses: actions-rs/cargo@v1
         with:

.github/workflows/nightly.yml

@@ -20,6 +20,7 @@ jobs:
           toolchain: nightly
           override: true
           components: rustfmt, clippy
+      - uses: Swatinem/rust-cache@v1
       - name: Install cargo-sort
         uses: actions-rs/install@v0.1
         with:

.github/workflows/stable.yml

@@ -19,6 +19,7 @@ jobs:
           profile: minimal
           toolchain: stable
           override: true
+      - uses: Swatinem/rust-cache@v1
       - name: Run checks
         uses: actions-rs/cargo@v1
         with: