Two bugs fixed recently had no tests that would have failed before the
fix. Add direct regressions so either cannot silently return:
1. tb_chirp_controller Group 3b (multi-frame, C-3): run a second full
frame back-to-back after DONE and assert chirp_counter returns to 0,
frame 2 reaches GUARD_TIME after exactly CHIRP_MAX/2 long chirps,
and frame 2 reaches DONE. Before the fix, chirp_counter held at
CHIRP_MAX after frame 1, the LONG_LISTEN -> GUARD guard (=CHIRP_MAX/2-1)
never matched, and frame 2 ran extra chirps until the 6-bit counter
wrapped — these checks fail loudly if that regresses.
2. tb_usb_data_interface frame-sync width + value pins: assert
$bits(uut.sample_counter) >= 15 and uut.NUM_CELLS == 15'd16384.
Protects against reintroducing the 12-bit / 2048-cell constants
that fired 8 false frame-start markers per real 512 x 32 frame.
Regression: 32/32 PASS; USB TB 89 -> 91 checks.
27c9c22ad2