Add more tests for the 1st and 2nd assignments

01-tree_successor/cpp/tree_successor_more_tests.cpp

01-tree_successor/python/tree_successor_more_tests.py

01-tree_successor/task.md

02-splay_operation/cpp/splay_operation_more_tests.cpp

02-splay_operation/python/splay_operation_more_tests.py

02-splay_operation/task.md