Upload one part of Bluetooth device values

One gzip NDJSON part (at most 64 MiB, never truncated), one characteristic value a standard Bluetooth health device sent per line: {"at": "<RFC 3339 arrival time with offset>", "char": "2a37", "value": "<hex>", "session": "<id of the connection>", "device": {"name", "manufacturer", "model", "firmware"}, "device_user": <index>} (device and device_user optional; the line format is in docs/connectors/bluetooth.md; ohs-bridge and the Swift and Kotlin SDKs write it). The server decodes heart rate with RR intervals, blood pressure, weight, body composition, glucose, temperature and pulse oximetry; other characteristics are stored and not mapped. The part is refused with 400, and nothing is stored, when a line breaks the format; a value that does not decode is a failed record of its line only. Same headers, limits and answers as the Apple Health upload. Re-sending the same part is safe: the answer is 200 with duplicate: true. Other bytes under a (day, batch, part) already stored are a 409, and so is a part sent while this provider's data is being deleted for the user (nothing is kept; send it again once the deletion job is done). Each instance processes a bounded number of uploads at once; above it the answer is 503 with Retry-After.