Suggest instruments

Suggests instruments for the instruments field of an Audio-to-MIDI request. The detector listens to sampled windows of the audio, reported in windows, several times each. Suggestions need review: instruments is exhaustive, so a missing instrument cannot appear in the transcription and a wrong one pulls notes onto the wrong part. Review every suggestion, not only the low-agreement ones, and add anything the detector missed; a missing instrument carries no score at all. Upload the audio once with POST /v2/assets and pass the same asset to this route and to the transcription; for a URL source the response returns the stored copy's asset_id. A detection is free when an Audio-to-MIDI request that succeeds passes its instrument_detection_id. Unused detections are free up to 10 per account in any 24 hours. Past that a detection costs up to 50 credits (never more than transcribing the same audio), charged on success, and those credits come off the transcription that later uses it within 30 days, in the same billing period. Organization keys cannot call this route yet. Send max_credits: 0 to run only when free: past the allowance the request fails with max_credits_exceeded and charges nothing. The same account, audio content and detector revision returns the cached answer free.