Fix fan speed control, plain JSON datagram parsing, and direct UDP state confirmation

[FlashWreck]

Summary of Changes

• Fix Speed Control: Changed async_set_percentage to send {"speed": speed} directly rather than bundling power: True. Atomberg BLDC microcontroller firmware evaluates commands using single-key parsing; bundling power caused speed adjustments to be ignored by the motor controller.
• Support Plaintext & Hex JSON Datagrams: Updated parse_datagram in udp.py to handle both standard JSON and hex-encoded JSON datagrams. Added hexadecimal MAC validation before presence beacon splitting to avoid corrupting plaintext JSON packets into {"device.
• Direct UDP Response Capture: Updated send_command in udp.py with a non-blocking timeout to capture immediate UDP responses from port 5600, enabling sub-50ms command confirmations.
• Optimistic State & Transport Sync: Setting speed now reflects power = True in local optimistic state immediately, and direct responses eliminate false-positive 1.5s Wi-Fi timeouts and premature BLE fallbacks.

Testing & Verification

• Hardware Tested: Verified on physical hardware (Atomberg Renesa Halo Smart R3) with Home Assistant 2026 over LAN UDP. Speed control, power on/off, and state confirmation are working reliably.
• Script Tests: Validated standalone unit tests across command building, state bitfield decoding (speeds 1–6, power on/off), and datagram parsing.