protocol change : COM_STMT_PREPARE avoids sending parameters metadata

COM_STMT_PREPARE protocol is :

• COM_STMT_PREPARE_OK.
• If number of parameters (count of '?' placeholders) > 0:
  • For each parameter:
    • column definition packet.
  • If !DEPRECATE_EOF eof_packet.
• If prepared statement returns result set and number of result set columns > 0:
  • For each column:
    • column definition packet.
  • If !DEPRECATE_EOF eof_packet.

While the parameter count is useful information for connectors, the parameter metadata packets themselves are not. They consistently indicate generic string types and provide no meaningful information for connectors.

Most connectors already skip these packets.

The goal of this change is to eliminate the parameter metadata section when a new capability flag is enabled.

Benchmark results (tested on two local computers using the attached patch):

• Current implementation: 444.461 operations/second
• With patch (connector capability enabled): 460.190 operations/second