Modern collections: immutable factories, unmodifiable views and sequenced collections #95

Goal: clarify which collection you actually get from the modern APIs.

Show:

• List.of / List.copyOf (immutable, null-hostile) vs Collections.unmodifiableList (view that reflects changes)
• Stream.toList() vs Collectors.toList() (mutability guarantees)
• SequencedCollection: getFirst/getLast/reversed() across List, LinkedHashSet, LinkedHashMap

Where: FirstSteps/src/test/java/pl/mperor/lab/java/idiom