Fix wrong marshalling for call* & eval responses

[Speshal71]

The problem

The array of bytes we get after marshalling of *Result might be different from original sequence of bytes it was umarshalled from. This the case at least for call* and eval responses if they return scalar or array of scalars. This happens because:

• The documentation specifies response data as an MP_OBJECT:
  https://www.tarantool.io/en/doc/2.11/dev_guide/internals/iproto/requests/#iproto-call
• Instead the library always expects it to be an array of tuples and forcefully wraps it :
  

  go-tarantool/result.go

  Line 86 in 6f8008d

  r.Data[i] = []interface{}{val}