fix: remove duplicates from symbol table, forbid var redeclarations

[LeanSerra]

Description

This PR modifies the symbol table creation logic by:

• Storing the table as a global variable in the form of a Vec, every time we parse a symbol we push it to this vector
• If compilation is successful or we exit with an error we first dump the table into a file
• When parsing the variable declarations inside init {} if we find a symbol that is already in the table we exit with an error.
  This PR also modifies the parsing of negative floats and integers:
• The enum variants NumberNegativeInt and NumberNegativeInt were removed in favor of using i64 and f32 to store negatives.

[MatiBarcia]

LGTM!