ci: add Cargo registry/git caching and keep target/ between projects

Add actions/cache@v4 for ~/.cargo/registry and ~/.cargo/git to all 4
matrix CI workflows (anchor, native, pinocchio, quasar). Cache key
uses Cargo.toml/Cargo.lock hashes with OS-based restore-keys fallback.

Also stop deleting target/ between project builds in anchor.yml — the
shared dependencies (anchor-lang, solana-program, etc.) only need to
compile once. node_modules cleanup is kept since each project has its
own JS deps.

Author: mikemaccana-edwardbot

.github/workflows/anchor.yml

@@ -108,6 +108,15 @@ jobs:
       failed_projects: ${{ steps.set-failed.outputs.failed_projects }}
     steps:
       - uses: actions/checkout@v5
+      - name: Cache Cargo registry and git
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+          key: cargo-${{ runner.os }}-${{ hashFiles('**/Cargo.toml', '**/Cargo.lock') }}
+          restore-keys: |
+            cargo-${{ runner.os }}-
       - uses: pnpm/action-setup@v4
       - uses: heyAyushh/setup-anchor@v4.999
         with:
@@ -166,7 +175,6 @@ jobs:
             if ! anchor build; then
               echo "::error::anchor build failed for $project"
               echo "$project: anchor build failed" >> $GITHUB_WORKSPACE/failed_projects.txt
-              rm -rf target
               cd - > /dev/null
               return 1
             fi
@@ -175,13 +183,13 @@ jobs:
             if ! anchor test; then
               echo "::error::anchor test failed for $project"
               echo "$project: anchor test failed" >> $GITHUB_WORKSPACE/failed_projects.txt
-              rm -rf target node_modules
+              rm -rf node_modules
               cd - > /dev/null
               return 1
             fi
 
             echo "Build and tests succeeded for $project."
-            rm -rf target node_modules
+            rm -rf node_modules
             cd - > /dev/null
             return 0
           }

.github/workflows/native.yml

@@ -107,6 +107,15 @@ jobs:
       failed_projects: ${{ steps.set-failed.outputs.failed_projects }}
     steps:
       - uses: actions/checkout@v5
+      - name: Cache Cargo registry and git
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+          key: cargo-${{ runner.os }}-${{ hashFiles('**/Cargo.toml', '**/Cargo.lock') }}
+          restore-keys: |
+            cargo-${{ runner.os }}-
       - uses: pnpm/action-setup@v4
       - name: Use Node.js
         uses: actions/setup-node@v5

.github/workflows/pinocchio.yml

@@ -107,6 +107,15 @@ jobs:
       failed_projects: ${{ steps.set-failed.outputs.failed_projects }}
     steps:
       - uses: actions/checkout@v5
+      - name: Cache Cargo registry and git
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+          key: cargo-${{ runner.os }}-${{ hashFiles('**/Cargo.toml', '**/Cargo.lock') }}
+          restore-keys: |
+            cargo-${{ runner.os }}-
       - uses: pnpm/action-setup@v4
       - name: Use Node.js
         uses: actions/setup-node@v5

.github/workflows/quasar.yml

@@ -109,6 +109,15 @@ jobs:
       failed_projects: ${{ steps.set-failed.outputs.failed_projects }}
     steps:
       - uses: actions/checkout@v5
+      - name: Cache Cargo registry and git
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+          key: cargo-${{ runner.os }}-${{ hashFiles('**/Cargo.toml', '**/Cargo.lock') }}
+          restore-keys: |
+            cargo-${{ runner.os }}-
       - name: Setup build environment
         id: setup
         run: |