Add module internal to exports

[habetuz]

This PR adds a module internal to the list of exports. It contains all non-private functions (no trailing _) that are not exported in the top level module.

This gives packages users to style glossarium more easily, because, for example, default implementations from glossarium can still be used.

closes #193

[habetuz]

I also added two entries to the .gitignore I thing should be included. Let me know if I should revert this.

[quachpas]

@habetuz thanks for the patch! I'm working on the themes atm and I believe I could release 0.6.0 with the themes soonish.

If that's not the case, I'll merge this. Sorry for the annoyance.

[habetuz]

Sure, as you can read in my issue, I found a different workaround for my specific issue. So no need to hurry!

[amandeavor]

I tested the current head (de8f8eb) locally: all 43 Tytanic tests pass and the advanced documentation compiles with Typst 0.13.1. Importing the filtered module through the package entrypoint also compiles successfully.

Two small follow-ups would strengthen this before merge:

• default-group-break appears twice in the internal import list.
• A compile-only public-API test importing internal from glossarium.typ would protect these exports from silently disappearing later, since the existing tests import themes/default.typ directly.

I opened #202 before noticing this existing PR. I am closing mine to avoid splitting the same work; its tests/public-api/test.typ can be adapted to cover the internal module if useful.