fix: preserve comment placement in formatter

[ivov]

Comments now stay attached to the element the user wrote them on, instead of being moved out of enclosing braces, merged onto adjacent lines, swapped past #[attr], or migrated to the next sibling.

fn f(
  a: int,
  // between params
  b: int,
) -> int {
  a + b
}

Includes refactoring the formatter into submodules for maintainability.

[github-actions]

Released in lisette-v0.1.24