This refactor includes the following changes:
- Refactor similar tests using `types::for_each` to remove redundant code;
- Explicitly include the missing header `type_algorithms.h` in some test files;
- Some tests scattered in different test functions with ad-hoc names
(e.g., `test5()`, `test6()`) but belong to the same kind are now grouped
into one function (`test_struct_array()`).
