test(streams): harden take() ack tests against event-loop timing (fix PyPy flake)

[wbarnha]

Description

Fixes a flaky-test failure seen on the PyPy 3.11 CI leg (e.g. run
29672563646,
surfaced on #690). Four stream.take() tests failed with:

if not event.ack.called:
>   assert event.message.acked
E   assert False

Root cause

stream.take() acks the events it consumes from a background task. The
tests asserted the ack had happened after exactly two await asyncio.sleep(0)
yields:

await asyncio.sleep(0)
await asyncio.sleep(0)
if not event.ack.called:
    assert event.message.acked

On slower interpreters (notably PyPy) that background task hasn't run within
two event-loop ticks, so event.message.acked is still False and the
assertion flakes. The tests' own comments already hinted at this fragility
("need one sleep on 3.6.0–3.6.6; need two on 3.6.7 :-/"). It is not a product
regression — every CPython leg (3.10–3.14) passed, and the run went green on
re-run.

Fix

Introduce a small wait_for_stream_ack() helper that polls for the ack
(up to a 1s timeout) instead of assuming a fixed number of ticks, and use it in
the four affected tests:

• test_take
• test_take_wit_timestamp
• test_take_wit_timestamp_wit_simple_value
• test_take_wit_timestamp_without_timestamp_field

The existing assertions are left unchanged, so a genuinely missing ack still
fails the test with the same signal once the timeout elapses — this only
removes the timing race, not the coverage.

Verified locally: all four tests pass.

🤖 Generated with Claude Code

---

Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.15%. Comparing base (ade8a09) to head (03e5fde).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #709   +/-   ##
=======================================
  Coverage   94.15%   94.15%           
=======================================
  Files         104      104           
  Lines       11136    11136           
  Branches     1201     1201           
=======================================
  Hits        10485    10485           
  Misses        550      550           
  Partials      101      101           

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