Implement an Iterator API

[andrewthecodertx]

The current hash table API provides essential functions for inserting, looking up, and deleting key-value pairs. However, it lacks a mechanism for iterating over the elements currently in the table.

Iteration is a common and necessary feature for many use cases, such as:

• Dumping all key-value pairs for debugging.
• Serializing the contents of the table.
• Performing an operation on every element.

Suggestion:
Implement an iterator API. A common C pattern for this is to define an iterator struct and a set of functions to control it:

// Opaque iterator struct
typedef struct HashTableIterator HashTableIterator;

// Creates a new iterator for the table
HashTableIterator* hash_table_iterator_create(HashTable* table);

// Advances the iterator and returns the next key-value pair
// Returns false when there are no more items.
bool hash_table_iterator_next(HashTableIterator* iter, void** key, void** value);

// Destroys the iterator
void hash_table_iterator_destroy(HashTableIterator* iter);

This would significantly enhance the utility of the library.