Fix HTTPException body mapping when extra-info key is body

[Copilot]

HTTPException.body could remain empty because Python exception mapping only read response_body from DuckDB error extra-info. Some HTTP errors now surface payload under body, so the attribute was silently unset.

• Exception field mapping

  • Update HTTP exception translation to accept both extra-info keys:
    • legacy: response_body
    • current/alternate: body
  • This preserves backward compatibility while correctly populating HTTPException.body for newer payloads.

• Test expectation alignment

  • Adjust HTTPFS exception assertion to validate body as a string instead of assuming it is always empty.

} else if (entry.first == "response_body" || entry.first == "body") {
    e.attr("body") = entry.second;
}

[afeld]

Opened upstream: duckdb#614