v4.0.0

• feat!: upgrade to support Dart ^2.19.0

• feat: additional lint rules:

  • always_put_required_named_parameters_first
  • collection_methods_unrelated_type
  • combinators_ordering
  • dangling_library_doc_comments
  • enable_null_safety
  • implicit_call_tearoffs
  • library_annotations
  • unnecessary_library_directive
  • use_string_in_part_of_directives

• refactor: remove deprecated lint rules:

  • always_require_non_null_named_parameters
  • avoid_returning_null
  • avoid_returning_null_for_future