[stcc4] Add driver for Sensirion STCC4 CO2 sensor

[will-tm]

What does this implement/fix?

Add support for the Sensirion STCC4 miniature CO₂ sensor based on thermal conductivity measurement.

The STCC4 features a dedicated I²C controller interface for an onboard SHT4x sensor, providing
automatic temperature/humidity compensation and readings alongside CO₂ concentration. For boards
without an onboard SHT4x, external RHT compensation is supported via temperature_source and
humidity_source configuration options.

Implementation details aligned with the official Sensirion embedded driver.

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)
• Developer breaking change (an API change that could break external components)
• Code quality improvements to existing code or addition of tests
• Other

Related issue or feature (if applicable):

• N/A

Pull request in esphome-docs with documentation (if applicable):

• [stcc4] Add documentation for Sensirion STCC4 CO2 sensor esphome-docs#6108

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040
• BK72xx
• RTL87xx
• LN882x
• nRF52840

Example entry for config.yaml:

# With onboard SHT4x (typical eval kit / breakout board)
sensor:
  - platform: stcc4
    co2:
      name: "CO2 Concentration"
    temperature:
      name: "Temperature"
    humidity:
      name: "Humidity"
    ambient_pressure_compensation: 1013
    update_interval: 60s


# Without onboard SHT4x (external compensation)
sensor:
  - platform: sht4x
    temperature:
      name: "Temperature"
      id: sht4x_temp
    humidity:
      name: "Humidity"
      id: sht4x_humidity

  - platform: stcc4
    co2:
      name: "CO2 Concentration"
    temperature_source: sht4x_temp
    humidity_source: sht4x_humidity
    update_interval: 60s

Checklist:

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

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[github-actions]

To use the changes from this PR as an external component, add the following to your ESPHome configuration YAML file:

external_components:
  - source: github://pr#14037
    components: [stcc4]
    refresh: 1h

---

(Added by the PR bot)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.08%. Comparing base (5bb863f) to head (ae9124d).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #14037      +/-   ##
==========================================
- Coverage   74.11%   74.08%   -0.03%     
==========================================
  Files          55       55              
  Lines       11588    11588              
  Branches     1577     1577              
==========================================
- Hits         8588     8585       -3     
- Misses       2598     2600       +2     
- Partials      402      403       +1     

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