Finding declarations in an injected language.

I am writing a plugin for a custom language that is injected into python string literals. Imagine something like this:

code = [ 
    "$foo = 3",    // My language is injected in these string literals
    "$bar = $foo", // command clicking $foo should jump to the definition in the previous line.
]

The custom language plugin tutorial shows finding all declarations by finding all the files with your language extension in the project and then searching them: link. This doesn't work in this case as the injected `PsiFile`s are not found. I did find this post from 10 years ago asking the same question but it didn't really recieve an answer.

Hopefully sometthing has changed in the last decade/there is a different way of achieving my desired behavior.

Thanks!