Cache RowDescription

[elbaro]

Client                              Server
  │                                   │
  │─── Parse ────────────────────────>│
  │<───────────────── ParseComplete ──│
  │                                   │
  │─── Bind ─────────────────────────>│
  │<───────────────── BindComplete ───│
  │                                   │
  │─── Describe (optional) ──────────>│
  │<───────────────── ParameterDesc ──│  (if statement)
  │<───────────────── RowDescription ─│  (or NoData)

The same prepared statement with different binds return the same RowDescription if we always request the binary format.
RowDescription can be stored within PreparedStatement. Also, the user can manually hint like stmt.set_row_description(..)