Fix PathTrie copy constructor and assignment

[nawaz1991]

Summary

• fix memory leak in PathTrie copy constructor and assignment operator
• guard DeleteNode against null pointer
• add regression tests for PathTrie copy semantics

Testing

• cmake -S . -B build -DBUILD_TESTS=ON (fails: Could NOT find GTestSrc)

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https://chatgpt.com/codex/tasks/task_e_6847f3376a08832390a3860110be76b9

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

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