Wait for the required EcoFlow reports in each collection

A Bluetooth collection listened for a fixed 10 seconds and returned the data that arrived. If a required report was late, the snapshot missed shared measurements without notice.

Each decoder now tracks the reports behind the shared measurements. A collection listens for 10 seconds, then until those reports arrive, for at most 30 seconds in total. The new ef_missing_measurements field names the reports that did not arrive. The server log shows one line each time that list changes.

The diagnostic tool now uses the River 2 heartbeat list from the decoder.

README.md

@@ -101,6 +101,12 @@ failed one. It reads a serial BMS every 5 seconds and retries a failed serial
 read after 1 second. Unavailable devices are omitted from the response. Only the
 first request after startup waits, until each device completes one read attempt.
 
+Each Bluetooth read listens for 10 seconds. If a required report is still
+missing, the read continues until the report arrives, for at most 30 seconds in
+total. A read that reaches this limit returns a partial snapshot. Its
+`ef_missing_measurements` field names the missing reports, and the server log
+shows one line each time that list changes.
+
 #### Diagnostics
 
 Stop the server before connecting directly. Scan and collect reports from both Rivers: