Expose RTL_433 contact states in Home Assistant discovery

[dajiaohuang]

Description

Add Home Assistant binary sensor discovery for RTL_433 contact fields closed, contact_open, and opened. The closed field is inverted so a closed sensor state maps to Home Assistant off; contact_open and opened keep their reported polarity. All three use the neutral opening device class.

This addresses the missing discovery mappings discussed in #2375. The separate RTL_433_ESP decoding work mentioned there remains upstream.

Validation: git diff --check and focused source checks pass. A local PlatformIO build was attempted but could not run because PlatformIO is unavailable (pio is not installed and Python has no platformio module).

Checklist:

• The pull request is done against the latest development branch
• Only one feature/fix was added per PR and the code change compiles without warnings (local PlatformIO build unavailable)
• I accept the DCO.

[1technophile]

Thanks, you need to add opening into 'availableHASSClasses'

[dajiaohuang]

The requested follow-up is prepared locally: HASS_CLASS_OPENING is defined as "opening" in config_mqttDiscovery.h and included in availableHASSClasses.

Both PlatformIO release builds pass with this patch: esp32dev-rtl_433 and nodemcuv2-rf. ESP8266's upstream elf2bin.py emits Python SyntaxWarnings, so this is not a warning-free claim.

I have not validated the discovery payload on physical hardware. The contribution checklist requires hardware testing; the follow-up remains unpublished until that requirement can be satisfied. The existing PR head is still 76a52734640079ab2f57530f99ae793eef52e72b, so its CI does not validate these two local additions.