Return zst Decoder to sync.pool when finished

defered close for dec was broken due to shadowed variable so removed.
Added defer close in the go func that calls cache.Put
With this change we can handle higher load on the server without crash due
GOMAXPROCS.

server/grpc_bytestream.go

@@ -15,7 +15,6 @@ import (
 	"github.com/buchgr/bazel-remote/v2/cache"
 	"github.com/buchgr/bazel-remote/v2/cache/disk/casblob"
 
-	"github.com/klauspost/compress/zstd"
 
 	"github.com/buchgr/bazel-remote/v2/utils/zstdpool"
 	syncpool "github.com/mostynb/zstdpool-syncpool"
@@ -367,12 +366,6 @@ func (s *grpcServer) Write(srv bytestream.ByteStream_WriteServer) error {
 	resourceNameChan := make(chan string, 1)
 
 	cmp := casblob.Identity
-	var dec *zstd.Decoder
-	defer func() {
-		if dec != nil {
-			dec.Close()
-		}
-	}()
 
 	go func() {
 		firstIteration := true
@@ -454,6 +447,7 @@ func (s *grpcServer) Write(srv bytestream.ByteStream_WriteServer) error {
 				}
 
 				go func() {
+					defer rc.Close()
 					err := s.cache.Put(srv.Context(), cache.CAS, hash, size, rc)
 					putResult <- err
 				}()