Fix getter/setter for polymorphic module-level variables

[krystophny]

Fixes #374.

For module-level variables of class types (derived types with type-bound procedures), the generated getter/setter pointed the *_ptr_type payload directly at the module variable. For class types the payload is a *_wrapper_type holding a class pointer, so the generated wrapper failed to compile. Route module-level access through the wrapper obj pointer, matching the existing code path for class-typed components of derived types. The handle encoding for class-typed values is now ptr_type -> wrapper_type -> obj everywhere, consistent with the method-call convention; the new example verifies this by calling a type-bound method on the retrieved global.

Adds examples/issue374_polymorphic_global with the reproducer from the issue: get/set of both a plain derived-type global and a polymorphic one, plus a method call on the retrieved global.

Verification

Test fails on main

$ cd examples/issue374_polymorphic_global && make test
  195 |     global_testclass_ptr%p => main_global_testclass
      |     1~~~~~~~~~~~~~~~~~~~~~
Error: Different types in pointer assignment at (1); attempted assignment of TYPE(testclass) to TYPE(testclass_wrapper_type)
  214 |     main_global_testclass = global_testclass_ptr%p
Error: Cannot convert TYPE(testclass_wrapper_type) to TYPE(testclass) at (1)
make: *** [Makefile:30: f2py] Error 1

Test passes after fix

$ cd examples/issue374_polymorphic_global && make test
python tests.py
....
----------------------------------------------------------------------
Ran 4 tests in 0.000s

OK

Class-related examples all pass after the change: fortran_oo, issue235_allocatable_classes, issue258_derived_type_attributes, issue254_getter, derivedtypes, mockderivetype, extends, class_names. Unit tests: 38 passed (2 pre-existing test_parse_dnad failures addressed separately).

@jameskermode ready for review.

[krystophny]

Wheel CI failed for cp312/cp313 on Linux: numpy 2.5 ships only manylinux_2_28 wheels, so the default manylinux2014 container built numpy from source and failed its gcc >= 10.3 check. Included a one-line workflow fix building Linux wheels in the manylinux_2_28 image.