fix(http): retry incomplete completion body transport failures

[rudycelekli]

What changed

An HTTP connection can close before the declared completion body finishes. aiohttp raises ClientPayloadError in that case; it currently escapes HttpProvider.send_message instead of using the existing connection-error retry contract.

Normalize this payload transport error alongside ClientConnectionError. Existing retry counts, backoff, malformed-complete-JSON response errors and successful completion parsing are retained. The retrieval path already handles ClientError separately.

Native proof and checks

• Actual owned asyncio HTTP server receives the public provider request, closes the first response halfway through its declared body, and can return a complete valid response on retry. Before3 native cases fail/2 controls pass; after5 pass covering recovery, zero retries, exhaustion, complete malformed JSON without retry and ordinary success.
• Final native18 focused passes with existing HTTP response-shape/retrieval controls.
• Signed d0e1eaf: Ruff0.16.9, Bandit, layout and all11 example fixtures pass; Mypy advisory retains1 existing error.
• Exact official fork Python3.10/3.11/3.12 jobs all success: https://github.com/rudycelekli/iFixAi/actions/runs/37544073558 . Upstream PR checks are observed separately.

This is a native transport/retry test, not evidence of external model efficacy. Current-main7f1f68b and all authored feedback/file overlaps checked before publication. #199 handles HTTP status retries on different lines of this file; #184 handles other native SDK transport classes. No duplicate source change. SSH signature and DCO verified.

AI assistance: Codex helped investigate, implement and test; the complete source and actual native evidence were independently reviewed before publication.