Add Docker Buildx caching for TiDB component images

Add Buildx caching steps for tidb, pd, and tikv Docker images.
Each component is cached separately per version using GHA cache backend.

Author: zph

.github/workflows/main.yml

@@ -220,6 +220,51 @@ jobs:
           echo "version=${VERSION}" >> $GITHUB_OUTPUT
           echo "TiDB version for this test: ${VERSION}"
       
+      - name: Set up Docker Buildx for TiDB
+        if: contains(matrix.target, 'tidb')
+        uses: docker/setup-buildx-action@v3
+      
+      - name: Cache TiDB Docker images using Buildx
+        if: contains(matrix.target, 'tidb')
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: Dockerfile.tidb
+          push: false
+          tags: pingcap/tidb:v${{ steps.extract-tidb-version.outputs.version }}
+          build-args: |
+            TIDB_COMPONENT=pingcap/tidb
+            TIDB_VERSION=v${{ steps.extract-tidb-version.outputs.version }}
+          cache-from: type=gha,scope=tidb-v${{ steps.extract-tidb-version.outputs.version }}
+          cache-to: type=gha,mode=max,scope=tidb-v${{ steps.extract-tidb-version.outputs.version }}
+      
+      - name: Cache PD Docker image using Buildx
+        if: contains(matrix.target, 'tidb')
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: Dockerfile.tidb
+          push: false
+          tags: pingcap/pd:v${{ steps.extract-tidb-version.outputs.version }}
+          build-args: |
+            TIDB_COMPONENT=pingcap/pd
+            TIDB_VERSION=v${{ steps.extract-tidb-version.outputs.version }}
+          cache-from: type=gha,scope=pd-v${{ steps.extract-tidb-version.outputs.version }}
+          cache-to: type=gha,mode=max,scope=pd-v${{ steps.extract-tidb-version.outputs.version }}
+      
+      - name: Cache TiKV Docker image using Buildx
+        if: contains(matrix.target, 'tidb')
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: Dockerfile.tidb
+          push: false
+          tags: pingcap/tikv:v${{ steps.extract-tidb-version.outputs.version }}
+          build-args: |
+            TIDB_COMPONENT=pingcap/tikv
+            TIDB_VERSION=v${{ steps.extract-tidb-version.outputs.version }}
+          cache-from: type=gha,scope=tikv-v${{ steps.extract-tidb-version.outputs.version }}
+          cache-to: type=gha,mode=max,scope=tikv-v${{ steps.extract-tidb-version.outputs.version }}
 
       - name: Run tests {{ matrix.target }}
         env: