tuya_light: fix float->int conversion while setting color temperature

[kswt]

What does this implement/fix?

This PR fixes the conversion of the color temperature (CT) value between the components light and tuya_light. Light uses float datatype, but tuya_light uses int. In order to send to Tuya device exactly the same value that was read from it before, converted value must be rounded instead of simple int casting.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes esphome/issues#4669

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040

Example entry for config.yaml:

esp8266:
  board: nodemcuv2

logger:
  baud_rate: 0

uart:
  rx_pin: GPIO3
  tx_pin: GPIO1
  baud_rate: 115200

# Register the Tuya MCU connection
tuya:

light:
  - platform: "tuya"
    name: "Remez Leda"
    switch_datapoint: 20
    dimmer_datapoint: 22
    max_value: 1000
    color_temperature_datapoint: 23
    color_temperature_max_value: 1000
    cold_white_color_temperature: 154 mireds
    warm_white_color_temperature: 333 mireds
    color_temperature_invert: true

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).