Preserve using-declaration access for inherited methods

[guitargeek]

When GetClassDecls<CXXMethodDecl> walked a class's decls and hit a UsingShadowDecl whose target is a method, it pushed the target CXXMethodDecl from the base class. The target's getAccess() returns the access in the base (e.g. protected); the elevated access carried by the using-declaration (public in the introducing class) was silently lost. Consumers like CPyCppyy filter on IsPublicMethod, so a republished overload such as

class Base   { protected: void foo(int, int); };
class Derived: public Base {
public:
    using Base::foo;
    void foo(int);
};

would never reach the Python proxy - calling derived.foo(1, 2) from cppyy raised TypeError: takes at most 1 arguments (2 given) (cppyy issue compiler-research/cppyy#220).

Push the UsingShadowDecl itself (for the non-constructor case; constructor-using-shadows still go through findInheritingConstructor) and teach CheckMethodAccess to consult USD->getAccess(). A small UnwrapUsingShadowToFunction helper unwraps the shadow at the entry of every API that downcasts a TCppFunction_t to FunctionDecl (return type, arg counts/types/names/defaults, signature, IsConst/Static/Virtual/Constructor/Destructor/Templated/Explicit, function address, operator arity).

MakeFunctionCallable keeps the unwrapped target as the wrapped function but threads a relaxAccessControl flag into make_wrapper when the caller passed a using-shadow: the generated wrapper still references the target by its original qualified name (e.g. ((Base*)obj)->Base::foo(...)), so access control has to be relaxed during wrapper compilation for it to compile. The runtime call is well-defined because the using-declaration made the member reachable through the derived class.

Adds a FunctionReflection_GetClassMethods_UsingShadowAccess regression test covering both the public-promoted case from the issue and a protected-using control case (which must stay hidden).

Fixes: compiler-research/cppyy#220

[codecov]

Codecov Report

❌ Patch coverage is 97.72727% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.83%. Comparing base (1ea28e2) to head (03c9439).

Files with missing lines	Patch %	Lines
lib/CppInterOp/CppInterOp.cpp	97.72%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #995      +/-   ##
==========================================
+ Coverage   82.78%   82.83%   +0.05%     
==========================================
  Files          15       15              
  Lines        5048     5069      +21     
==========================================
+ Hits         4179     4199      +20     
- Misses        869      870       +1     

Files with missing lines	Coverage Δ
lib/CppInterOp/CppInterOp.cpp	89.00% <97.72%> (+0.04%)	⬆️

Files with missing lines	Coverage Δ
lib/CppInterOp/CppInterOp.cpp	89.00% <97.72%> (+0.04%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[vgvassilev]

Why not using UnwrapUsingShadowToFunction?