Add Sperax P3 Max (wi-linktech WLT6200) protocol support

[mcdax]

Adds a third protocol backend (alongside FTMS and WiLink) for the Sperax P3 Max walking pad (BLE name SPERAX_P3MAX). The device uses a wi-linktech WLT6200 module speaking a custom framed protocol on vendor service 0xFFF0 — it is not FTMS (0x1826) and not the legacy KingSmith WiLink protocol (0xFE00).

Requested in hass-walkingpad#3.

Protocol

Fully documented in docs/sperax-p3max-protocol.md.

F5 | LEN | 00 | CMD | ARGS | CRC16 | FA

• Byte-stuffing: body bytes 0xF0–0xFF are sent as F0 (byte & 0x0F)
• CRC-16: poly 0xA327, init 0xFFFF, reflected, little-endian
• Commands: hello 0x01, run 0x15 (speed = km/h×10, incline 0–2), vibration 0x16 (level 1–4), status poll 0x19
• The device only streams status while polled, so the backend runs a keep-alive poll loop.

Reverse-engineered from a full HCI snoop capture of a real P3 Max session.

Changes

• sperax.py (new) — SperaxController backend + frame codec (crc16/encode/decode) + 0x19 status parser + poll loop
• const.py — Sperax UUIDs, SPERAX_NAME_PREFIXES, ProtocolType.SPERAX
• controller.py — name/service auto-detection + dispatch; new set_incline() / set_vibration() (Sperax-only)
• __init__.py — export SperaxController and Sperax constants
• tests/test_sperax_codec.py (new) — hardware-free codec/parser tests
• docs/sperax-p3max-protocol.md (new) — full protocol reference

The unified WalkingPadController API (connect/start/set_speed/stop/…) works unchanged, so downstream consumers (e.g. hass-walkingpad) need no changes.

Verification

• 7/7 unit tests pass (pytest tests/test_sperax_codec.py)
• decode() validates 146/146 real captured frames; encode() round-trips every captured command frame byte-for-byte (incl. stuffing)
• ruff clean on all added/changed files

Not yet confirmed on hardware

• Speed range assumed 0.5–6.0 km/h (capture only reached 3.0; no readable range characteristic on this device)
• Status distance/duration/steps map to raw counters that aren't unit-verified yet — speed, belt state and vibration level are verified

🤖 Generated with Claude Code