Panic in csv.writer with QUOTE_STRINGS or QUOTE_NOTNULL

Summary

csv.writer panics when quoting is set to csv.QUOTE_STRINGS or
csv.QUOTE_NOTNULL.

Both constants are exposed by RustPython, but the writer path still reaches a
todo!() implementation for these quote styles.

Reproducer

import csv
import io

buf = io.StringIO()
csv.writer(buf, quoting=csv.QUOTE_STRINGS).writerow(["x", 1, None, ""])
print(repr(buf.getvalue()))

buf = io.StringIO()
csv.writer(buf, quoting=csv.QUOTE_NOTNULL).writerow(["x", 1, None, ""])
print(repr(buf.getvalue()))

Expected

CPython exits normally and produces:

'"x",1,,""\r\n'
'"x","1",,""\r\n'

QUOTE_STRINGS quotes fields whose original value is a string, while None
is written as an empty unquoted field.

QUOTE_NOTNULL quotes every field except None, which is written as an empty
unquoted field.

A single empty field produced from None should raise csv.Error:

csv.writer(io.StringIO(), quoting=csv.QUOTE_STRINGS).writerow([None])
csv.writer(io.StringIO(), quoting=csv.QUOTE_NOTNULL).writerow([None])

Actual

RustPython panics with:

thread 'main' panicked at crates/stdlib/src/csv.rs:...:
not yet implemented

The panic comes from the QuoteStyle::Strings / QuoteStyle::Notnull mapping
inside the native _csv implementation.

Python Documentation

csv.QUOTE_STRINGS and csv.QUOTE_NOTNULL are documented quoting constants:

https://docs.python.org/3/library/csv.html#csv.QUOTE_STRINGS
https://docs.python.org/3/library/csv.html#csv.QUOTE_NOTNULL