NOTE: We ensures that block's ids are unique.

- Separate the Const part of the Var in AST
- Begin to implement the SpellArgument getter (add methods to State)
- Named exports of some top-level structs/enums

[AST] Differenciate from parser span and ast span, and add convertion to get ast span for each of ast elements

Should be enaugh to parse the expressions, only need to implement some functions in the parser::utils module