[3.13] gh-120221: Support KeyboardInterrupt in asyncio REPL (GH-123795) (#123799)

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.
(cherry picked from commit 033510e11d)

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

Lib/test/test_repl.py

@@ -242,6 +242,7 @@ class TestInteractiveInterpreter(unittest.TestCase):
     def test_asyncio_repl_is_ok(self):
         m, s = pty.openpty()
         cmd = [sys.executable, "-I", "-m", "asyncio"]
+        env = os.environ.copy()
         proc = subprocess.Popen(
             cmd,
             stdin=s,
@@ -249,7 +250,7 @@ class TestInteractiveInterpreter(unittest.TestCase):
             stderr=s,
             text=True,
             close_fds=True,
-            env=os.environ,
+            env=env,
         )
         os.close(s)
         os.write(m, b"await asyncio.sleep(0)\n")
@@ -270,7 +271,7 @@ class TestInteractiveInterpreter(unittest.TestCase):
             proc.kill()
             exit_code = proc.wait()
 
-        self.assertEqual(exit_code, 0)
+        self.assertEqual(exit_code, 0, "".join(output))
 
 class TestInteractiveModeSyntaxErrors(unittest.TestCase):