PasteBurstTextArea(
self,
**kwargs: Any = {},
)TextAreaTextArea that detects paste-like keystroke bursts.
Subclasses drive the state machine from their own _on_key by calling the
helper methods here, and override the policy hooks
(_in_slash_command_context, _dispatch_burst_payload) as needed. The base
inserts a flushed burst verbatim; collapsing into placeholders is layered on
by CollapsingPasteTextArea.