[Bug] stylelint customSyntax postcss-lit deletes custom variables

First of all big thanks for fixing the main issue with variables inside string literals in css files for lit components.

The bug happens when you are using both a linter (to cut long lines of css into multiple lines) and stylelint with customSyntax postcss-lit in the following scenario:

let's assume we have the following css (single line css selector):
.long-class-name-container.${veryLongVariableNameAddedHere} .small-image-container span ${anotherVeryLongVariableNameAddedHere} img {
width: 100%;
height: 100%;
}

This will get parsed after linting into:
.long-class-name-container.${veryLongVariableNameAddedHere}
.small-image-container
span
${anotherVeryLongVariableNameAddedHere}
img {
width: 100%;
height: 100%;
}

And after stylelint into:
.general-takeover-container./* missing variable veryLongVariableNameAddedHere here*/
.small-image-container
span
/* missing variable anotherVeryLongVariableNameAddedHere here*/
img {
width: 100%;
height: 100%;
}

This is not happening when for example we have only one ${variable} at the end with "{" and gets parsed on the last line like:
.long-class-name-container .small-image-container span ${anotherVeryLongVariableNameAddedHere} {

into .long-class-name-container
.small-image-container
span
${anotherVeryLongVariableNameAddedHere} {
width: 100%;
height: 100%;
}

The issue is in the custom syntax parser for postcss-lit, which processes CSS inside template literals. Look at the parsing logic in the source files (likely in src/ or lib/) to see how it handles line breaks and variable interpolation. The bug appears when a CSS selector with multiple interpolated variables is split across lines. Start by reproducing the described scenario with a test file, then trace through the parsing to see where the variable tokens are lost.

Scritto dal modello di indicizzazione a partire dal testo della issue.