Fix overruns test to avoid return-beats-ctxc race

Turns out that py3.11 might be so fast that iterating a EoC-ed
`MsgStream` 1k times is faster then a `Context.cancel()` msg
transmission from a parent actor to it's child (which i guess makes
sense). So tweak the test to delay 5ms between stream async-for iteration
attempts when the stream is detected to be `.closed: bool` (coming in
patch) or `ctx.cancel_called == true`.

tests/test_context_stream_semantics.py

@@ -8,6 +8,7 @@ sync-opening a ``tractor.Context`` beforehand.
 # from contextlib import asynccontextmanager as acm
 from itertools import count
 import platform
+from pprint import pformat
 from typing import (
     Callable,
 )
@@ -815,7 +816,10 @@ async def echo_back_sequence(
     # NOTE: ensure that if the caller is expecting to cancel this task
     # that we stay echoing much longer then they are so we don't
     # return early instead of receive the cancel msg.
-    total_batches: int = 1000 if wait_for_cancel else 6
+    total_batches: int = (
+        1000 if wait_for_cancel
+        else 6
+    )
 
     await ctx.started()
     # await tractor.breakpoint()
@@ -834,8 +838,23 @@ async def echo_back_sequence(
         )
 
         seq = list(seq)  # bleh, msgpack sometimes ain't decoded right
-        for _ in range(total_batches):
+        for i in range(total_batches):
+            print(f'starting new stream batch {i} iter in child')
             batch = []
+
+            # EoC case, delay a little instead of hot
+            # iter-stopping (since apparently py3.11+ can do that
+            # faster then a ctxc can be sent) on the async for
+            # loop when child was requested to ctxc.
+            if (
+                stream.closed
+                or
+                ctx.cancel_called
+            ):
+                print('child stream already closed!?!')
+                await trio.sleep(0.05)
+                continue
+
             async for msg in stream:
                 batch.append(msg)
                 if batch == seq:
@@ -846,15 +865,18 @@ async def echo_back_sequence(
 
                 print('callee waiting on next')
 
+            print(f'callee echoing back latest batch\n{batch}')
             for msg in batch:
-                print(f'callee sending {msg}')
+                print(f'callee sending msg\n{msg}')
                 await stream.send(msg)
 
-    print(
-        'EXITING CALLEEE:\n'
-        f'{ctx.canceller}'
-    )
-    return 'yo'
+    try:
+        return 'yo'
+    finally:
+        print(
+            'exiting callee with context:\n'
+            f'{pformat(ctx)}\n'
+        )
 
 
 @pytest.mark.parametrize(
@@ -916,8 +938,8 @@ def test_maybe_allow_overruns_stream(
                 wait_for_cancel=cancel_ctx,
                 be_slow=(slow_side == 'child'),
                 allow_overruns_side=allow_overruns_side,
-            ) as (ctx, sent):
 
+            ) as (ctx, sent):
                 assert sent is None
 
                 async with ctx.open_stream(
@@ -945,10 +967,10 @@ def test_maybe_allow_overruns_stream(
 
                 if cancel_ctx:
                     # cancel the remote task
-                    print('sending root side cancel')
+                    print('Requesting `ctx.cancel()` in parent!')
                     await ctx.cancel()
 
-            res = await ctx.result()
+            res: str|ContextCancelled = await ctx.result()
 
             if cancel_ctx:
                 assert isinstance(res, ContextCancelled)