Support temperature-range climate destinations

[vasi786]

Summary

Adds support for heating-oriented Home Assistant climate destinations that
expose target_temp_low / target_temp_high instead of a single
temperature target.

This fixes compatibility with devices such as Plugwise Emma Wired Pro when
exposed through Zigbee2MQTT.

Behavior

• Existing single-target destinations remain unchanged.
• Range destinations:
  • use target_temp_low as the current heating target;
  • write the calculated ClimateSync setpoint to target_temp_low;
  • preserve the existing target_temp_high;
  • clamp the calculated lower target to the existing upper target when needed.
• Source climate behavior is unchanged.
• Range target changes trigger immediate reevaluation.
• Invalid range upper targets fail safely without sending a service call.

Testing

• Full suite: 110 passed
• Added coverage for:
  • unchanged single-target behavior;
  • range target reading;
  • preserving target_temp_high;
  • range upper-bound clamping;
  • invalid target_temp_high;
  • range target change reevaluation.

There is one pre-existing Python 3.14 unawaited-coroutine warning in the resync
test harness when running with -W error; this PR does not modify that test.

Manual verification

For climate.emma_wired_pro, this fails:

action: climate.set_temperature
target:
  entity_id: climate.emma_wired_pro
data:
  temperature: 23.5

while this succeeds

action: climate.set_temperature
target:
entity_id: climate.emma_wired_pro
data:
target_temp_low: 23.5
target_temp_high: 26

[vasi786]

Tested successfully on the actual device.

Setup:

• Home Assistant
• Plugwise Emma Wired Pro
• Emma connected through Zigbee2MQTT
• ClimateSync destination: climate.emma_wired_pro
• Versatile Thermostat source climates
• 0.5 °C rounding with ceiling

Real-device test:

• Emma current temperature: 23.6 °C
• Main Bedroom current: 23.3 °C
• Main Bedroom target: 24.1 °C
• Source delta: +0.8 °C
• ClimateSync calculated destination setpoint: 24.5 °C

Emma then reported:

24.5 °C - 26.0 °C

So target_temp_low was updated to 24.5 °C while the existing target_temp_high remained unchanged at 26.0 °C.

ClimateSync reported:

• Destination Current Target: 24.5 °C
• Status: ok