feat: zstd performance improvements

the lock in that once per decode/encode is expensive, so just do it once
at init

Signed-off-by: bo <bo.blanton@gmail.com>

zstd.go

@@ -1,28 +1,16 @@
 package sarama
 
 import (
-	"sync"
-
 	"github.com/klauspost/compress/zstd"
 )
 
-var (
-	zstdDec *zstd.Decoder
-	zstdEnc *zstd.Encoder
-
-	zstdEncOnce, zstdDecOnce sync.Once
-)
+var zstdDec, _ = zstd.NewReader(nil)
+var zstdEnc, _ = zstd.NewWriter(nil, zstd.WithZeroFrames(true))
 
 func zstdDecompress(dst, src []byte) ([]byte, error) {
-	zstdDecOnce.Do(func() {
-		zstdDec, _ = zstd.NewReader(nil)
-	})
 	return zstdDec.DecodeAll(src, dst)
 }
 
 func zstdCompress(dst, src []byte) ([]byte, error) {
-	zstdEncOnce.Do(func() {
-		zstdEnc, _ = zstd.NewWriter(nil, zstd.WithZeroFrames(true))
-	})
 	return zstdEnc.EncodeAll(src, dst), nil
 }