Mirrors the Slack precedent (register_slack_action_handler): plugins queue
a factory at register() time; the Telegram adapter invokes each factory
with (application, adapter) at connect() time, before the core handlers
register, so pattern-scoped plugin handlers take precedence for their own
updates while everything else falls through unchanged. Factories are
isolated — a raising plugin cannot prevent Telegram from connecting.
Unblocks standalone plugins that need PTB update types the core adapter
doesn't route (Telegram Business API secretary bots, custom callback
prefixes, chat-member events) without touching core files.
7c4cde9e82