fix(amux): detect nested data.status in async video poll

[duanbing]

Problem

Every Doubao-Seedance video generation polled amux for the full ASYNC_TASK_TIMEOUT (3600s) and then failed with did not complete within 3600s — even though the render succeeded on amux's side (and was billed upstream, ~87k tokens per discarded task).

Root cause

The universal poll endpoint GET /v1/video/generations/{task_id} returns:

{"code":"success","data":{"status":"succeeded","url":"https://cdn.amux.ai/…mp4"}}

But poll_async_result read the root-level status and only matched "completed":

• status is nested under data.status → root read was always None/""
• amux reports success as "succeeded", not "completed"

So the loop never hit a terminal arm and ran to the timeout. parse_urls already handled data.url, so only the status detection was broken.

Fix

• Read status from data.status, falling back to the root for a flat shape.
• Accept "succeeded"/"completed" (Done) and "failed"/"error" (Failed), reading the reason from data.error.message.
• Extracted the logic into a pure classify_poll helper with unit tests: nested succeeded, nested failed w/ reason, pending states (queued/in_progress/unknown/empty), and the flat-shape fallback. Also a parse_urls test for data.url.

Verified against the real captured amux response. cargo check -p tensorzero-core + clippy are clean.

Note: cargo test's lib target is currently red on main for an unrelated reason (test initializers missing the newer InferenceParams.media_generation field in chat_completion/dicl/variant). The amux test module itself compiles. Not addressed here to keep this PR scoped.

🤖 Generated with Claude Code

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