Parse Sensor Packet

Parse a binary sensor packet in Python. Packet format: [STX][ID][DATA1][DATA2][CHK][ETX]. STX=0x02, ETX=0x03. The checksum is ID+DATA1+DATA2 modulo 256. Return parsed dictionary.

Constraints

• Packet length = 6.
• Validate STX and ETX.
• Validate checksum.
• Return dict {id, data1, data2}.
• Return None if invalid.