🧪 Add missing tests for Hashmap map_clear

[tiziano88]

🎯 What: The testing gap in map_clear has been addressed by adding a unit test to oak_benchmarks/benchmark/memory/hashmap.rs.
📊 Coverage: The test validates the map_clear function by creating a HashMapBenchmark, populating it, and asserting it becomes empty again after calling map_clear.
✨ Result: Increased test coverage for the memory benchmark component, ensuring correct implementation of the map_clear operation.

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PR created automatically by Jules for task 7813068359130113485 started by @tiziano88

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