ClientCache implements an LRU cache and acts as the gatekeeper for logging client metadata for incoming gRPC streams. This ticket focuses on using the existing LRUCache to implement a thread-safe ClientCache, where:

• The constructor forwards the maximum cache size to the constructor of LRUCache. By default, we will set this to 65,536, reserving about 1 MB of memory for the cache.
• The add method inserts clientId into the underlying cache:
• If the clientId already exists, the cache is updated and the add method returns false.
• Otherwise, it returns true.

class ClientCache {
	explicit ClientCache(size_t maxSize);
	bool add(const UUID& clientId) = 0;
};