perf(grpc): switch to gRPC CodecV2 for improved performance

This PR updates the gRPC codec from v1 to v2, enhancing performance and reducing
memory allocations by utilizing a memory pool for encoded messages.

Refs:
- grpc/grpc-go#7356
- vitessio/vitess#16790

pkg/rpc/codec.go

@@ -1,35 +1,62 @@
 package rpc
 
 import (
-	gogoproto "github.com/gogo/protobuf/proto"
-	"github.com/golang/protobuf/proto" //nolint:staticcheck
 	"google.golang.org/grpc/encoding"
+	"google.golang.org/grpc/mem"
 )
 
 const name = "proto"
 
-type codec struct{}
+type gogoprotoMessage interface {
+	MarshalToSizedBuffer([]byte) (int, error)
+	Unmarshal([]byte) error
+	ProtoSize() int
+}
+
+var pool = mem.DefaultBufferPool()
+
+type codec struct {
+	fallback encoding.CodecV2
+}
 
-var _ encoding.Codec = codec{}
+var _ encoding.CodecV2 = &codec{}
 
 func init() {
-	encoding.RegisterCodec(codec{})
+	encoding.RegisterCodecV2(&codec{
+		fallback: encoding.GetCodecV2(name),
+	})
 }
 
-func (codec) Marshal(v interface{}) ([]byte, error) {
-	if m, ok := v.(gogoproto.Marshaler); ok {
-		return m.Marshal()
+func (c *codec) Marshal(v any) (mem.BufferSlice, error) {
+	if m, ok := v.(gogoprotoMessage); ok {
+		size := m.ProtoSize()
+		if mem.IsBelowBufferPoolingThreshold(size) {
+			buf := make([]byte, size)
+			if _, err := m.MarshalToSizedBuffer(buf[:size]); err != nil {
+				return nil, err
+			}
+			return mem.BufferSlice{mem.SliceBuffer(buf)}, nil
+		}
+
+		buf := pool.Get(size)
+		if _, err := m.MarshalToSizedBuffer((*buf)[:size]); err != nil {
+			pool.Put(buf)
+			return nil, err
+		}
+		return mem.BufferSlice{mem.NewBuffer(buf, pool)}, nil
 	}
-	return proto.Marshal(v.(proto.Message))
+	return c.fallback.Marshal(v)
 }
 
-func (codec) Unmarshal(data []byte, v interface{}) error {
-	if m, ok := v.(gogoproto.Unmarshaler); ok {
-		return m.Unmarshal(data)
+func (c *codec) Unmarshal(data mem.BufferSlice, v any) error {
+	if m, ok := v.(gogoprotoMessage); ok {
+		buf := data.MaterializeToBuffer(pool)
+		defer buf.Free()
+		return m.Unmarshal(buf.ReadOnlyData())
 	}
-	return proto.Unmarshal(data, v.(proto.Message))
+	return c.fallback.Unmarshal(data, v)
 }
 
-func (codec) Name() string {
+func (*codec) Name() string {
 	return name
 }