chore: clarify comment regarding offset

A full FlatBuffer structure would be:

- uoffset_t: root table offset (4 bytes)
- soffset_t: vtable offset in root table (4 bytes)
- uint16_t: vtable size (2 bytes)
- uint16_t: table size (2 bytes)

In total 12 bytes. We are only validating the data length
before trying to read the uoffset_t, not the full structure.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

Author: thevilledev

go/grpc.go

@@ -25,7 +25,8 @@ func (FlatbuffersCodec) Marshal(v interface{}) ([]byte, error) {
 
 // Unmarshal parses the wire format into v.
 func (FlatbuffersCodec) Unmarshal(data []byte, v interface{}) error {
-	// Need at least 4 bytes to read the root UOffsetT
+	// Need at least 4 bytes to read the root table offset (UOffsetT).
+	// Vtable soffset_t and metadata are read later during field access.
 	if len(data) < SizeUOffsetT {
 		return ErrInsufficientData
 	}