feat: add active scan interval for dynamic polling rate

[D34DC3N73R]

Introduce a separate polling interval that activates while a device is running, replacing the single static scan interval.

• Add CONF_ACTIVE_SCAN_INTERVAL constant (default 35s, min 30s, max 3600s); LG's API returns a 9006 rate-limit warning at exactly 30s
• Add LGEDevice._apply_scan_interval() which switches each device's coordinator between the idle and active interval based on is_on state; called after every poll so the transition is immediate on the next cycle
• Expose both intervals as config-category number entities and in the options flow so they can be adjusted from the UI without a reload
• Update _options_update_listener to re-apply per-device intervals when either setting changes, rather than blindly writing one delta to all coordinators