Overlap Azure OCR with local barcode decoding

[Szer]

Slow barcode decoding delays the Azure OCR request even though the two stages read the same image independently. Start the OCR task first, run the local barcode decoder, then await OCR before parsing the combined result. This overlaps network wait with CPU work while preserving local-barcode priority, one OCR request per recognition, and backend-failure handling. It needs no additional CPU worker.

Validation:

• All 45 OCR tests and 264 CouponHubBot integration tests pass. New cases cover deferred success, empty results, faults, cancellation, and synchronous OCR failure.
• All 2,201 original coupon images return identical recognition outputs before and after with the same mock OCR response.
• Five paired runs on five original images in a two-CPU ARM64 pod, with a simulated one-second OCR response, give the median end-to-end timings below. No paid Azure calls were made; these measurements demonstrate overlap rather than predict live Azure latency.

Original-image case	Sequential	Overlapped
Fast native read A	1.013 s	1.001 s
Fast native read B	1.012 s	1.000 s
Managed fallback success A	1.220 s	1.000 s
Managed fallback success B	1.498 s	1.000 s
Exhausted local search	1.974 s	1.000 s