test: distinguish nan none in test case (#11540)

* test: distinguish nan and none

[TD-14736]

* modify test framework for datetime

* fix 2-query/math_funcs.py

* fix 2-query/math_funcs.py

tests/parallel_test/cases.task

@@ -111,7 +111,7 @@
 ,,develop-test,python3 ./test.py -f 2-query/diff_funcs.py
 ,,develop-test,python3 ./test.py -f 2-query/TD-13246.py
 ,,develop-test,python3 ./test.py -f 2-query/TD-6347.py
-#,,develop-test,python3 ./test.py -f 2-query/math_funcs.py
+,,develop-test,python3 ./test.py -f 2-query/math_funcs.py
 ,,develop-test,python3 ./test.py -f 5-taos-tools/taosbenchmark/limit_offset_json.py
 ,,develop-test,python3 ./test.py -f 5-taos-tools/taosbenchmark/sml_json_alltypes.py
 ,,develop-test,python3 ./test.py -f 5-taos-tools/taosbenchmark/auto_create_table_json.py