plugin XEP-0166, XEP-0167, XEP-0234, XEP-0353: call events management to prepare for UI: - XEP-0166: add `jingle_preflight` and `jingle_preflight_cancel` methods to prepare a jingle session, principally used by XEP-0353 to create and cancel a session - XEP-0167: preflight methods implementation, workflow split in more methods/signals to handle UI and call events (e.g.: retract or reject a call) - XEP-0234: implementation of preflight methods as they are now mandatory - XEP-0353: handle various events using the new preflight methods rel 423

from typing import Optional

from twisted.words.xish import domish


class BaseError(Exception):
    namespace: str
    condition: str
    text: Optional[str]
    textLang: Optional[str]
    appCondition: Optional[domish.Element]

class StanzaError(BaseError):
    ...