allocate slice with struct once and decode into every item (#71)

otherwise every separate struct is allocated on heap, and later is copied into original array.

decoder.go

@@ -356,14 +356,13 @@ func DecodeStructSliceWithLimit[V any, H DecodablePtr[V]](d *Decoder, limit uint
  return nil, total, nil
  }
 
- value := make([]V, 0, lth)
+ value := make([]V, lth)
  for i := uint32(0); i < lth; i++ {
- val, n, err := DecodeStruct[V, H](d)
+ n, err := H(&value[i]).DecodeScale(d)
  total += n
  if err != nil {
  return nil, total, err
  }
- value = append(value, val)
  }
  return value, total, nil
 }