MySQL ERR packets can include a 5-byte SQLSTATE, but PyMySQL currently drops it when raising exceptions. This change preserves that protocol metadata on the exception object while keeping the existing exception args and string representation stable.

• Error packet parsing

  • Parse SQLSTATE from ERR packets in pymysql.err.raise_mysql_exception().
  • Continue decoding the human-readable message exactly as before.

• Exception surface

  • Attach the parsed value as exc.sqlstate.
  • Leave exc.args unchanged as (errno, message) to avoid breaking existing callers that depend on current formatting/tuple shape.
  • Default sqlstate to None when the server packet does not include it.

• Focused coverage

  • Add unit assertions for both packet shapes:
    • ERR packet with SQLSTATE
    • ERR packet without SQLSTATE

Example:

from pymysql import err

data = b"\xff\x15\x04#28000Access denied"

try:
    err.raise_mysql_exception(data)
except err.OperationalError as exc:
    assert exc.args == (1045, "Access denied")
    assert exc.sqlstate == "28000"