Implement out-of-process flow run pauses (#7863)

Co-authored-by: Zach Angell <42625717+zangell44@users.noreply.github.com>

src/prefect/exceptions.py

@@ -363,5 +363,5 @@ class FlowPauseTimeout(PrefectException):
     """Raised when a flow pause times out"""
 
 
-class PausedRun(BaseException):
+class PausedRun(PrefectSignal):
     """Signal raised when exiting a flow early for nonblocking pauses"""