Add __qualname__ tests

[gentlegiantJGC]

Description

Add tests for function and method __qualname__ attributes. I believe these tests will fail with the current implementation but they should pass. These are tests for the correct behaviour of #2059 and #5774

Suggested changelog entry:

• TODO.

[henryiii]

@rwgk I'd agree, the __qualname__ doesn't look right:

- module_func
+ pybind11_detail_function_record_v1_system_libstdcpp_gxx_abi_1xxx_use_cxx11_abi_1.module_func

[rwgk]

@rwgk I'd agree, the __qualname__ doesn't look right:

- module_func
+ pybind11_detail_function_record_v1_system_libstdcpp_gxx_abi_1xxx_use_cxx11_abi_1.module_func

Absolutely, I beat on this pretty hard already (4+ hours), but didn't get lucky: https://github.com/pybind/pybind11/issues/5774#issuecomment-3153805339