Avoid using jsoniter, move to fastjson (#8063)

This is to avoid using unsafe.Pointer type
code dependency for MinIO, this causes
crashes on ARM64 platforms

Refer #8005 collection of runtime crashes due
to unsafe.Pointer usage incorrectly. We have
seen issues like this before when using
jsoniter library in the past.

This PR hopes to fix this using fastjson

cmd/fs-v1-multipart.go

@@ -30,6 +30,7 @@ import (
 
 	"github.com/minio/minio/cmd/logger"
 	mioutil "github.com/minio/minio/pkg/ioutil"
+	"github.com/valyala/fastjson"
 )
 
 // Returns EXPORT/.minio.sys/multipart/SHA256/UPLOADID
@@ -456,7 +457,8 @@ func (fs *FSObjects) ListObjectParts(ctx context.Context, bucket, object, upload
 	}
 	for i, part := range result.Parts {
 		var stat os.FileInfo
-		stat, err = fsStatFile(ctx, pathJoin(uploadIDDir, fs.encodePartFile(part.PartNumber, part.ETag, part.ActualSize)))
+		stat, err = fsStatFile(ctx, pathJoin(uploadIDDir,
+			fs.encodePartFile(part.PartNumber, part.ETag, part.ActualSize)))
 		if err != nil {
 			return result, toObjectErr(err)
 		}
@@ -470,7 +472,16 @@ func (fs *FSObjects) ListObjectParts(ctx context.Context, bucket, object, upload
 		return result, err
 	}
 
-	result.UserDefined = parseFSMetaMap(fsMetaBytes)
+	parser := fsParserPool.Get()
+	defer fsParserPool.Put(parser)
+
+	var v *fastjson.Value
+	v, err = parser.ParseBytes(fsMetaBytes)
+	if err != nil {
+		return result, err
+	}
+
+	result.UserDefined = parseFSMetaMap(v)
 	return result, nil
 }