Add separate chaining to HashTable, add tests for HashTable, CircularLinkedList and Trie

[loiane]

Completes the remaining P1 items from the improvement plan.

HashTable — separate chaining collision handling

hash-table.ts previously silently overwrote values when two keys hashed to the same bucket. Replaced with a proper separate chaining implementation:

• Backing store changed from a sparse array to Map<number, KeyValuePair<V>[]>
• put: appends a new {key, value} to the bucket's chain, or updates the value if the key already exists
• get: traverses the chain at the bucket and returns the matching value, or undefined
• remove: removes the matching pair from the chain; deletes the bucket if it becomes empty
• toString: formats as {hash => [key: value, key: value, ...]} per bucket

Trie — bug fix in remove

Pre-existing bug: removing a word that is an extension of another word (e.g. 'card') would incorrectly prune the shared-prefix node and break search('car'). Fixed by adding an && !node.isEndOfWord guard in #removeWord so intermediate nodes that are themselves word endpoints are never deleted.

New test files (10 suites, 123 tests total)

File	Tests	What's covered
08-dictionary-hash/__test__/hash-table.test.ts	16	put/get/remove, collision handling, key update, toString
06-linked-list/__test__/circular-linked-list.test.ts	16	append/prepend/insert/remove/indexOf/clear/reverse, circular structure validation
12-trie/__test__/trie.test.ts	14	insert/search/startsWith/remove, prefix edge cases, shared-prefix removal