G522's 0x020D V2 uses a 5-byte band stride
[freq_hi, freq_lo, gain_i8, q_hi, q_lo] and a 13-byte getEQInfos
(gain bounds, gain_steps, format, xy, preset counts). Frequency and
Q are opaque u16 round-trip values — the u16->Hz and u16->Q mappings
need a LGHUB pcap to pin down (documented in
~/ghub/HEADSET_ADVANCED_PARA_EQ_WIRE_PROTOCOL.md).
get_advanced_eq_info now returns a dict with a `version` discriminator
and the union of V0/V1 and V2 fields; step_db is derived from the
gain_min/gain_max/gain_steps triple on V2 (0.05 dB/LSB on G522).
get_advanced_eq_params version-switches: V2 uses parse_v2_bands which
probes header length {5, 2, 0} until the tail is a clean multiple of
5, strips trailing all-zero terminator entries. V0/V1 falls through
to the legacy 3-byte stride so older devices still work.
HeadsetAdvancedEQ.build() no longer requires band_count from
getEQInfos (V2 doesn't advertise it); derives from getCustomEQ length
per the wire-protocol doc's recommendation. V2 band labels use
"Band N" since u16->Hz isn't confirmed. Read-only still — writes
stay gated until pcap confirms the encodings.
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