Add support for JCHENG SECURITY Contact and PIR sensors

[hertzg]

Summary

Add decoders for JCHENG SECURITY sensors:

• Contact Sensor (Jcheng-Contact): Door/window contact sensor with 16-bit ID, reports closed state, battery status, and event flag
• PassiveIR Sensor (Jcheng-PIR): PIR motion sensor with 12-bit ID, reports motion, tamper, and battery status

Both sensors use OOK PWM modulation at 433.92MHz with 25-bit messages.

Protocol Details

Contact Sensor (25 bits):

PPPP IIII IIII IIII IIII OBSX XX

• P: 4-bit preamble (0xF)
• I: 16-bit sensor ID
• O: is_on flag
• B: battery_ok
• S: state (1=closed, 0=open)

PIR Sensor (25 bits):

PPPP PPPP IIII IIII IIII TMBX XX

• P: 8-bit preamble (0xAA)
• I: 12-bit sensor ID
• T: tamper flag
• M: motion detected
• B: battery_low

Notes

• Decoders are disabled by default as there is no checksum/CRC in the protocol
• Users can enable with -R 292 (contact) or -R 293 (PIR)

Test data

I can provide test recordings for the Contact Sensor only. Unfortunately, I no longer have the PIR sensor device.

@zuckschwerdt: Would you prefer I remove the PIR decoder from this PR and submit it as Contact Sensor only? I can add the PIR decoder later if/when I have access to the device again.

Test plan

• Add test recordings for Contact Sensor to rtl_433_tests
• Verify decoding with actual sensor recordings

[zuckschwerdt]

Thanks! The code looks great. If there is no checksum and no advanced decoding I'd always recommend to use a flex decoder. Given that there is the 0xa/0xaa check it might warrant a full decoder though.