• `modernize-use-default-member-init` and `readability-redundant-member-init`
• Minor adjustments to `.clang-tidy` to improve syntax & remove redundancies
Random-access access to `List` when iterating is `O(n^2)` (`O(n)` when
accessing a single element)
* Removed subscript operator, in favor of a more explicit `get`
* Added conversion from `Iterator` to `ConstIterator`
* Remade existing operations into other solutions when applicable
