feat(parser): add support for parsing and replacing custom functions

[sgulseth]

Description

Add support for parsing custom functions! Currently it just replaces/inlines the function where it's used, from a typegen perspective it can end up being a lot of repetition, but this is step 1 and we can look into normalizing it later.

What to review

The parser mainly 😬

Testing

Added unit tests, and enabled groq test suite with custom functions 🖖

[sgulseth]

This change is part of the following stack:

• refactor: add inline function step to replace functions after parsing #308
  • feat(parser): add support for parsing and replacing custom functions #309 ◀

_{Change managed by git-spice.}