Add unordered_map, unordered_set, multiset, multimap

[AnshMNSoni]

Problem

The library has stl_map and stl_set, but is missing their hash-based (O(1) average) and multi-key variants. These are among the most used containers in C++ STL, especially in competitive programming.

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Missing Containers

Container	C++ Equivalent	Key Feature
unordered_map	std::unordered_map<K,V>	Hash map, avg O(1) lookup
unordered_set	std::unordered_set<T>	Hash set, avg O(1) lookup
unordered_multimap	std::unordered_multimap<K,V>	Hash map with duplicate keys
unordered_multiset	std::unordered_multiset<T>	Hash set with duplicate values
multiset	std::multiset<T>	Sorted set allowing duplicates
multimap	std::multimap<K,V>	Sorted map allowing duplicate keys

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Expected API (Example for unordered_map)

from pythonstl import unordered_map

um = unordered_map()
um.insert("key", 42)
print(um.find("key"))   # 42
print(um.count("key"))  # 1
um.erase("key")
print(um.size())        # 0

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Checklist

• unordered_map
• unordered_set
• unordered_multimap
• unordered_multiset
• multiset
• multimap
• Unit tests for each
• Docstrings with time complexity annotations

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Notes

• unordered_map and unordered_set should be prioritized as they are the most frequently used.
• multiset and multimap are natural extensions of the already existing stl_set and stl_map.