Improved error messages on parser failures

[AlexanderViand]

Adds better error messages on parser failures, for example:

Error: Error parsing operation: attribute expected
at line 8, column 52 (byte 422) near token exclamationIdent '!felt.type'
      "struct.member"() <{sym_name = "val", type = !felt.type}> {llzk.pub} : () -> ()

Also, vibe-coded by AI and zero testing, but @math-fehr wanted to have this here

[math-fehr]

I'll take care of this PR, but I'll actually change most of the code.
I think we want to create a new ParserError structure and return this instead of a String on all our parser errors.
While this works, it's only a bandage solution and I prefer writing the real thing first.