fix: Go 1.26 vet compliance, grpc build tag in proto gen

- Fix format string vet errors in db2_test.go and key_registry.go
  for Go 1.26 stricter printf checks
- Update pb/gen.sh to add //go:build grpc tag after protoc generation
  so protobuf types only compile with grpc tag (default uses ZAP
  native binary encoding from types_zap.go)

db2_test.go

@@ -241,7 +241,7 @@ func TestBigKeyValuePairs(t *testing.T) {
 				}
 				return item.Value(func(val []byte) error {
 					if len(val) == 0 {
-						log.Fatalf("key not found %q", len(key))
+						log.Fatalf("key not found %d", len(key))
 					}
 					return nil
 				})
@@ -378,7 +378,7 @@ func TestBigValues(t *testing.T) {
 				}
 				return item.Value(func(val []byte) error {
 					if len(val) == 0 || len(val) != len(data) || !bytes.Equal(val, data) {
-						log.Fatalf("key not found %q", len(key))
+						log.Fatalf("key not found %d", len(key))
 					}
 					return nil
 				})
@@ -602,7 +602,7 @@ func TestL0GCBug(t *testing.T) {
 			success++
 		}
 		if err != nil && err != ErrNoRewrite {
-			t.Fatalf(err.Error())
+			t.Fatalf("%s", err.Error())
 		}
 	}
 	// Ensure at least one GC call was successful.

key_registry.go

@@ -399,7 +399,7 @@ func storeDataKey(buf *bytes.Buffer, storageKey []byte, k *pb.DataKey) error {
 		// decrypting the datakey back.
 		if err2 = xor(); err2 != nil {
 			return y.Wrapf(err,
-				y.Wrapf(err2, "Error while decrypting datakey in storeDataKey").Error())
+				"%s", y.Wrapf(err2, "Error while decrypting datakey in storeDataKey").Error())
 		}
 		return err
 	}

pb/gen.sh

@@ -5,3 +5,7 @@
 
 go install google.golang.org/protobuf/cmd/protoc-gen-go@v1.31.0
 protoc --go_out=. --go_opt=paths=source_relative badgerpb4.proto
+
+# Add grpc build tag so protobuf types are only compiled when grpc tag is set.
+# The default (non-grpc) build uses native binary encoding from types_zap.go.
+sed -i.bak '1s/^/\/\/go:build grpc\n\n/' badgerpb4.pb.go && rm -f badgerpb4.pb.go.bak