Resolve "Parsing/Building : allow left arguments" ✨️

Closes #98 🐔️👍️
Approved-by: aalbert <augustin.albert@bleu-azure.fr>
Approved-by: loutr <l.ta-ma@proton.me>

🦀️🍰🦀️🍰🦀️🍰

* chore(parser): add coverage

* chore(parser): make more complex test

* feat(parser): more concise function `parse_args`

* fix(parser): use `try_fold` instead of ` fold`

* Apply 1 suggestion(s) to 1 file(s)

* chore(error): add new rules to parsing errors

* feat(std): use left-args in examples

* chore(parser): comment and test

* feat(parser): parse left-arguments

* feat(parser): add left-args to the syntax