Add StateVal conversion helpers and availability checks

[dmamelin]

StateVal Helpers

• New StateVal helpers wrap Home Assistant’s forgiving converters, so input_number.brightness.as_int(default=0) or sensor.timestamp.as_datetime() just work - no more manual int(...)/float(...) juggling or wrapping those casts in try/except.
• Added availability checks: .is_unknown(), .is_unavailable(), and .has_value() replace ad-hoc comparisons with unavailable/unknown.

Example (for illustration only):

@state_trigger("float(sensor.some_number)>10") #got error on unavailable/unknown
def old_style():
    try:
        sensor_value = int(sensor.another_sensor)
    except Exception:
        sensor_value = 0
    if sensor_value > 10 or binary_sensor.motion == "on":
        try:
            temperature = float(sensor.temperature)
            if temperature > 20:
                if climate.ac not in ["unavailable", "unknown"]: #check device online
                    climate.ac.set_temperature(temperature=sensor_value+10)
        except Exception:
            pass

@state_trigger("sensor.some_number.as_float(default=0)>10") # no error on unavailable/unknown
def new_style():
    sensor_value = sensor.another_sensor.as_int(default=0)
    
    if sensor_value > 10 or binary_sensor.motion.as_bool(False):
        temperature = sensor.temperature.as_float(-100)
        if temperature > 20 and climate.ac.has_value():
            climate.ac.set_temperature(temperature=sensor_value+10)

[craigbarratt]

This is awesome! Thanks for the PR.

[dmamelin]

Found a regression affecting state_active and as_*; working on a fix.