Adds HE SU decoding so a real BE550/iPhone capture (Wi-Fi 6/6E) decodes
instead of returning Unsupported:
- HeMimoControl: 5-octet HE MIMO Control parse (Nc/Nr/BW/grouping/codebook/
feedback-type/RU start+end), field offsets confirmed against WiPiCap.
- parse_he_action/parse_he_report producing HeBeamform.
- SU angle widths reuse the reference-validated (2,4)/(4,6); subcarrier count
derived from payload length (WiPiCap approach) rather than an HE RU table.
- HE MU/CQI feedback returns Unsupported (not decoded).
- Shared unpack_angles() now used by both VHT and HE.
4 new tests (HE MIMO parse, HE 2x2 length-derived round-trip, HE MU
unsupported) -> 24 lib tests pass; clippy -D warnings clean. Wiring HE into
the capture pipeline's report enum is a follow-up.
Co-Authored-By: claude-flow <ruv@ruv.net>