add parse_free method to Problem class, add test fubction #442

Job	Run time
Build and run tests (ubuntu-latest, 3.9)	4m 54s
Build and run tests (ubuntu-latest, 3.10)	4m 49s
Build and run tests (ubuntu-latest, 3.11)	4m 59s
Build and run tests (ubuntu-latest, 3.12)	5m 26s
Build and run tests (ubuntu-latest, 3.13)	4m 59s
Build and run tests (macos-13, 3.9)	7m 35s
Build and run tests (macos-13, 3.10)	7m 34s
Build and run tests (macos-13, 3.11)	5m 46s
Build and run tests (macos-13, 3.12)	7m 22s
Build and run tests (macos-13, 3.13)	11m 30s
Build and run tests (macos-latest, 3.9)	4m 11s
Build and run tests (macos-latest, 3.10)	3m 11s
Build and run tests (macos-latest, 3.11)	3m 46s
Build and run tests (macos-latest, 3.12)	3m 51s
Build and run tests (macos-latest, 3.13)	4m 57s
Build and run tests (windows-latest, 3.9)	8m 53s
Build and run tests (windows-latest, 3.10)	8m 37s
Build and run tests (windows-latest, 3.11)	8m 49s
Build and run tests (windows-latest, 3.12)	7m 58s
Build and run tests (windows-latest, 3.13)	9m 7s
	2h 8m 14s

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