Release driver-side references in PublisherModel before publishing

[ptomecek]

Summary

PublisherModel.__call__ held live references to the source result (data) and the extracted pub_data for the entire duration of the publisher's execution. When a publisher writes a large frame to a sink, it can build a sole-reference ownership carrier internally so the frame is freed before the terminal write drains — a peak-memory contract. But the outer method retaining data/pub_data defeated that ownership transfer from the outside, so the frame's refcount never dropped to zero during publisher(). Peak memory was roughly twice the frame size during the terminal write for any return_data=False sink-write publisher.

Fix

When return_data=False, the driver-side references are deleted before invoking the publisher, so the publisher can own the sole reference and free the frame during the write:

publisher.data = pub_data
if self.return_data:
    out = publisher()
    return data
del data, pub_data
out = publisher()
return self.result_type(value=out)

When return_data=True, references are retained because the source result must be returned. Behavior is otherwise unchanged.

Testing

Added regression tests using weakref + gc that verify the frame is collected during publisher() when return_data=False, and retained when return_data=True. The new return_data=False test was confirmed to fail on the pre-fix source. Full ccflow/tests/models suite passes (81 tests).

[github-actions]

Test Results

    1 files  ±0      1 suites  ±0   3m 8s ⏱️ +8s
1 330 tests +2  1 328 ✅ +2  2 💤 ±0  0 ❌ ±0 
1 336 runs  +2  1 334 ✅ +2  2 💤 ±0  0 ❌ ±0 

Results for commit a8b125d. ± Comparison against base commit 6a788a6.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.51%. Comparing base (6a788a6) to head (a8b125d).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #261      +/-   ##
==========================================
+ Coverage   93.48%   93.51%   +0.03%     
==========================================
  Files         176      176              
  Lines       20327    20361      +34     
  Branches     1350     1350              
==========================================
+ Hits        19002    19040      +38     
+ Misses       1052     1050       -2     
+ Partials      273      271       -2     

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