Restore last target temperature on ClimateCall mode switch

[Sammy1Am]

When handling a ClimateCall with a defined mode but no target_temperature, use the last-set target temperature for that mode. Update "last-set target temperature" every time the target temperature is received from the heatpump.

Desired behavior:

• Clicking the "Mode" button in HA to change mode will automatically change the target temperature to where it was last set for that mode.
• ANY explicit change to target temperature should override this behavior
  • From HA: Target temperature in ClimateCall takes precedence
  • From MHK: Target temperature is set directly without ClimateCall logic and "last-set" will be updated on refresh from heat pump
  • From IR: "Last-set" will be updated on refresh from heat pump

[Sammy1Am]

Closed in favor of this branch: https://github.com/muart-group/esphome/tree/upr-recallsetpoint Will (hopefully) be opened as a PR directly to upstream ESPHome, someday.