Sample every measurement exactly once, flagging losses in a warning
column rather than dropping them, so sample_index stays a valid
chip-time grid coordinate. Calibrate the true period before recording;
abort if no loss-free stretch exists.
Captures now store only raw counts plus a config header, with tesla and
both time bases reconstructed on load. Cycle count becomes the rate knob
(TMRC has no effect once it governs), raising the ceiling ~4x via
repeated-START reads and a shorter GIL switch interval.
