Add support for AL-KO smart charger devices (ALKO-CHARGER)

[budisek]

Summary

This PR adds support for AL-KO smart charger devices (e.g. C 200 Li 36V / model C38-4260) that are registered in the AL-KO inTOUCH app but were previously invisible in Home Assistant.

Root causes fixed

• API category filter — pyalko fetches devices with thingCategory=ALKO-ROBOLINHO, which silently excludes chargers and other non-mower device types. This PR overrides get_devices() in a subclass to remove the filter so all registered devices are returned.
• hasattr() checks — all attributes are defined as @property on ThingstateStateReported, so hasattr() always returned True regardless of what the device actually reports. Replaced throughout with direct key checks on the raw .attributes dict.

New entities for smart chargers

Sensors

• Input voltage (V) and frequency (Hz)
• Charger error code (0 = OK)
• Total operation time
• Per battery slot: level (%), voltage (V), charging current (A), temperature (°C), total charge cycles
• RSSI / signal strength

Binary sensors

• Per battery slot: inserted, charging
• Is Connected

Switches

• Eco Mode — reduces charging current to ~1.5 A (from ~3 A) for lower heat and longer battery life
• Battery 1 / 2 Storage Mode — ON sets charging limit to 60 % (recommended for winter / long-term storage), OFF restores 100 %

Side effects on existing mower support

• lawn_mower.py: fixed device filter so mower entities are not created for chargers
• button.py: fixed filter so Reset Blade Life button is not created for chargers
• All platforms: hasattr() → .attributes key checks (no functional change for mowers, just correctness)

Test plan

• Mower entities still appear and function correctly after update
• Smart charger device appears as a new HA device after update
• Charger sensors show correct values (input voltage ~230 V, frequency 50 Hz)
• Eco Mode switch toggles correctly in the AL-KO app
• Storage Mode switch sets 60 % / 100 % limit correctly in the AL-KO app
• Battery inserted / charging binary sensors update when battery is inserted and charging begins

Device tested

AL-KO C 200 Li 36V Smart Charger (model C38-4260, type ALKO-CHARGER)

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