Cache llvm-cov tool (#34)

Installing `cargo-llvm-cov` each time takes a long time and is wasteful.
Cache it the same way we cache `cargo-deny`.

| GH Action | Time before | Time after |
| ------------- | ------------- | ------------- |
| Coverage (PR) | [166
seconds](https://github.com/NethermindEth/rust-template/actions/runs/19867825551)
| [38
seconds](https://github.com/NethermindEth/rust-template/actions/runs/20507497399)
|
| Coverage (Push) | [87
seconds](https://github.com/NethermindEth/rust-template/actions/runs/19242367930)
|[ 18
seconds](https://github.com/NethermindEth/rust-template/actions/runs/20507478141)
|

Author: frozenspider

.github/workflows/coverage-pr.yml

@@ -19,7 +19,21 @@ jobs:
         with:
           ref: ${{ github.event.pull_request.head.sha }}
 
-      - run: cargo install cargo-llvm-cov
+      - name: Cache llvm-cov build
+        id: cache-llvm-cov
+        uses: actions/cache@v4
+        continue-on-error: false
+        with:
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            target/
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: ${{ runner.os }}-cargo-
+
+      - run: which cargo-llvm-cov || cargo install cargo-llvm-cov
       - run: rustup component add llvm-tools-preview
       - run: cargo llvm-cov --workspace --lcov --output-path lcov.info --ignore-filename-regex '^examples/'
 
@@ -71,9 +85,24 @@ jobs:
         with:
           ref: ${{ github.event.pull_request.base.sha }}
 
+      - name: Cache llvm-cov build
+        id: cache-llvm-cov
+        if: ${{ steps.base_art.outputs.found == 'false' }}
+        uses: actions/cache@v4
+        continue-on-error: false
+        with:
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            target/
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: ${{ runner.os }}-cargo-
+
       - name: Install cargo-llvm-cov (fallback path)
         if: ${{ steps.base_art.outputs.found == 'false' }}
-        run: cargo install cargo-llvm-cov
+        run: which cargo-llvm-cov || cargo install cargo-llvm-cov
 
       - name: Install llvm-tools (fallback path)
         if: ${{ steps.base_art.outputs.found == 'false' }}

.github/workflows/coverage.yml

@@ -14,7 +14,21 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - run: cargo install cargo-llvm-cov
+      - name: Cache llvm-cov build
+        id: cache-llvm-cov
+        uses: actions/cache@v4
+        continue-on-error: false
+        with:
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            target/
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: ${{ runner.os }}-cargo-
+
+      - run:  which cargo-llvm-cov || cargo install cargo-llvm-cov
       - run: rustup component add llvm-tools-preview
       - run: cargo llvm-cov --workspace --lcov --output-path lcov.info --ignore-filename-regex '^examples/'