Support for .yml.liquid file formatting

Is your feature request related to a problem? Please describe.
The current plugin does not properly format .yml.liquid files, which are YAML files containing Liquid template syntax. This leads to inconsistent formatting and potential errors in our project's configuration files.

Describe the solution you'd like
Add support for .yml.liquid files, allowing the plugin to correctly format both the YAML structure and the embedded Liquid syntax without breaking the file's overall structure.

Describe alternatives you've considered
We've considered using separate YAML and Liquid formatters, but this approach is cumbersome and doesn't provide a seamless solution for our mixed-syntax files.

Checklist

• I have checked and made sure that the proposal adheres to this plugin's principles

Additional context
This feature would greatly improve the development workflow for projects using Shopify themes or similar setups where YAML and Liquid are frequently combined.

Start by reading docs/prettier-plugin-liquid/principles/index.md and locating the plugin's formatter entry point for YAML and Liquid files. Trace how compound extensions are classified, then verify that .yml.liquid files preserve both YAML structure and embedded Liquid syntax without breaking either format.