gh-120221: Support KeyboardInterrupt in asyncio REPL (#123795)

This switches the main pyrepl event loop to always be non-blocking so that it
can listen to incoming interruptions from other threads.

This also resolves invalid display of exceptions from other threads
(gh-123178).

This also fixes freezes with pasting and an active input hook.

Lib/test/test_pyrepl/support.py

@@ -161,8 +161,8 @@ class FakeConsole(Console):
     def forgetinput(self) -> None:
         pass
 
-    def wait(self) -> None:
-        pass
+    def wait(self, timeout: float | None = None) -> bool:
+        return True
 
     def repaint(self) -> None:
         pass