The user-facing macro is now PYBIND11_SMART_HOLDER_TYPE_CASTERS.

https://github.com/rwgk/rwgk_tbx/commit/a2c2f88174a30f5de80d7d26e0f77c7b60f5fb85

These tests are from experimenting, and for demonstrating UB in pybind11 multiple inheritance handling ("first_base"), to be fixed later.

Removing debugging comments (GET_STACK, GET_INT_STACK). cast.h is identical to current master again, pybind11.h only has the generic_type::initialize(..., &type_caster_generic::local_load) change.

Folding convert_type into lvalue_ref and rvalue_ref paths. Some smart_holder_type_caster_load cleanup.

Adding smart_holder_type_caster_load::loaded_as_shared_ptr, currently bypassing smart_holder shared_ptr tracking completely, but the tests pass and are sanitizer clean.

Pure renaming of function and variable names, for better generalization when convoluting with inheritance. NO functional changes.

Pure renaming of function names in test_classh_inheritance, similar to the systematic approach used in test_class_wip. NO functional changes.

Removing stray isinstance<T>(src): it interferes with the py::module_local feature. Adding missing #includes.

First pass adjusting try_implicit_casts and try_load_foreign_module_local to capture loaded_v_h, but untested and guarded with pybind11_failure("Untested"). This was done mainly to determine general feasibility. Note the TODO in pybind11.h, where type_caster_generic::local_load is currently hard-coded. test_classh_wip and test_classh_inheritance still pass, as before.

Folding in modified_type_caster_generic_load_impl, just enough to pass test_class_wip. test_classh_inheritance is still failing, but with a different error: [RuntimeError: Incompatible type (as_raw_ptr_unowned).]