🧪 [testing improvement] Fix and enhance HashMap resize test coverage

[void0x14]

🎯 What: The testing gap addressed: Missing Test for HashMap Resize Logic and a dangling pointer issue in an existing test.
📊 Coverage: What scenarios are now tested: A specific test exact resize boundary at 75% load factor ensures accurate transition from 8 to 16 capacity on insertion of the 7th item. The stress test was updated to test dynamically allocated memory and properly trigger thousands of resizes to catch collisions properly.
✨ Result: The improvement in test coverage: Resize exact limits are strictly confirmed to have proper capacity tracking and element survival logic.

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PR created automatically by Jules for task 5649406687465840401 started by @ulac000000

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