Only extract flight data after all basic messages get merged

currently, `extractFlightData()` is called after parsing each message, which causes the first valid "ifs" in the extractFlightData() function to make that the data that is used.

i.e: `extractAttitudes()` prioritizes AHR2, but if that is not available, and ATT is, ATT is used instead.

related to #253

Start by tracing the message-parsing flow into extractFlightData(), then inspect how extractAttitudes() chooses between AHR2 and ATT. Verify that flight data extraction waits until all basic messages are merged, and confirm the final selection follows the intended fallback priority; review related issue #253 for context.

Written by the indexing model from the issue text.