refactor(ion): Refactor to fix clippy lints

fix: clippy lints

closes issue: none

test: regression tested in tests and with cargo +nightly test --lib

refactor: Lots of refactoring to fix the lints, including a more major rework of parser::statement. See commit log.

docs: N/A, no functional changes or additions.

perf: No difference as far as I can see.