Block detectable I/O in the event loop (#48387)

We added a warning when this happens last April and gave developers
a year to fix the instability. We now prevent the instability by
raising RuntimeError when code attempts to do known I/O in the
event loop instead of the executor.

We now provide a suggestion on how to fix the code that is causing
the issue.

homeassistant/util/async_.py

@@ -136,6 +136,10 @@ def check_loop() -> None:
         found_frame.lineno,
         found_frame.line.strip(),
     )
+    raise RuntimeError(
+        f"I/O must be done in the executor; Use `await hass.async_add_executor_job()` "
+        f"at {found_frame.filename[index:]}, line {found_frame.lineno}: {found_frame.line.strip()}"
+    )
 
 
 def protect_loop(func: Callable) -> Callable:

tests/util/test_async.py

@@ -78,7 +78,7 @@ async def test_check_loop_async():
 
 async def test_check_loop_async_integration(caplog):
     """Test check_loop detects when called from event loop from integration context."""
-    with patch(
+    with pytest.raises(RuntimeError), patch(
         "homeassistant.util.async_.extract_stack",
         return_value=[
             Mock(
@@ -107,7 +107,7 @@ async def test_check_loop_async_integration(caplog):
 
 async def test_check_loop_async_custom(caplog):
     """Test check_loop detects when called from event loop with custom component context."""
-    with patch(
+    with pytest.raises(RuntimeError), patch(
         "homeassistant.util.async_.extract_stack",
         return_value=[
             Mock(