Python `watch_address` uses bare `list[str]` type hint and `= None` default — should use `Optional[List[str]]`

[realfishsam]

Inconsistency

watch_address in the Python SDK uses the bare list[str] generic (Python 3.9+ only) with a = None default. This is both a compatibility issue (breaks Python 3.8) and a type-correctness issue (list[str] does not include None, so the annotation is wrong for the given default).

Current (PMXT)

sdks/python/pmxt/client.py line ~2030:

def watch_address(self, address: str, types: list[str] = None):

Two problems:

1. list[str] as a generic requires Python ≥ 3.9; the rest of the SDK imports List from typing for 3.8 compatibility.
2. The annotation list[str] does not permit None, but the default is None. The correct annotation is Optional[List[str]].

Expected (CCXT convention)

CCXT Python uses typing.List and typing.Optional throughout for 3.8 compatibility. Consistent with the rest of sdks/python/pmxt/client.py and sdks/python/pmxt/models.py:

from typing import List, Optional

def watch_address(self, address: str, types: Optional[List[str]] = None):

Impact

Code using this method will fail to import or raise a TypeError on Python 3.8. Static type checkers (mypy) will flag the None default as incompatible with the list[str] annotation.

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Found by automated PMXT ↔ CCXT API consistency audit