Add light_on_off_toggle option for ON/OFF buttons

[csmarshall]

Summary

Adds a new light_on_off_toggle configuration option that changes ON and OFF button behavior from discrete turn_on/turn_off to toggle.

• New boolean config option light_on_off_toggle (default: false)
• When enabled, both ON and OFF buttons check current light state and flip it
• Works with all Pico types: 3BRL (tap toggles), P2B and 2B (tap toggles, hold still ramps in the original direction)
• Follows existing config patterns (_normalize_bool, defaults merging, per-device override)

Use case

When a Pico controls a single light or light group, it's convenient to have either button toggle regardless of current state — especially in the dark where you don't want to think about which button you're reaching for. This is a common request in the HA community for Pico remotes.

Changes

• config.py — new light_on_off_toggle field on PicoConfig, parsed via _normalize_bool
• actions/light_actions.py — press_on/press_off and release_on/release_off check the flag; new _toggle() method reads entity state
• README.md — config table, dedicated docs section, behavior table updated, sample config example

Example

pico_link:
  devices:
    - name: Living Room Remote
      type: 3BRL
      lights:
        - light.living_room_lamp
      light_on_off_toggle: true

Backward compatible

Defaults to false — no behavior change for existing configs.