refactor: Consolidate all test files into tests/ directory

- Moved 5 test files from root to tests/:
  - verify_random.prox
  - verify_all_features.prox
  - test_to_string.prox
  - test_debug.prox
  - debug_logical.prox

- Merged test/ directory into tests/ (moved 5 files):
  - debug_keywords.prox
  - test_builtins.prox
  - test_datatypes.prox
  - test_keywords.prox
  - test_random.prox

- Removed empty test/ directory to avoid confusion
- All tests now centralized in tests/ directory

Author: ProgrammerKR