Vague exception thrown when redefining classes in debug mode

[AutonomicPerfectionist]

Describe the bug
I discovered that some tests do not enable debug mode for the entire test; they only set it in one subsection,
which is not preserved in any tests or sections above it. An example is here:

CMakePPLang/tests/class/class.cmake

Line 10 in 4427a52

set(CMAKEPP_LANG_DEBUG_MODE ON)

Upon enabling it for the entire test, I discovered that multiple tests started failing because they were redefining classes, but the exception was a type error in the signature of the cpp_decl() function:

Assertion: class is convertible to desc failed.
CMakePPLang/cmake/cmakepp_lang/class/class_decl.cmake:63 (cpp_assert_signature)

It appears that since the class is defined, the type of MyClass changes from desc to class, which fails the signature check. Might be a good idea to explicitly disallow redefining classes, or if it's desired to change the type in the signature to str