Add two unit tests to check that inherited methods are hidden by overrides

tests/errors/cypclass_hidden_overridden_methods.pyx

+# mode: error
+# tag: cpp, cpp11, pthread
+# cython: experimental_cpp_class_def=True, language_level=2
+
+cdef cypclass A:
+    void foo(self, int a):
+        pass
+    
+cdef cypclass B(A):
+    void foo(self, int a, int b):
+        pass
+
+def test_hidden_overridden_methods():
+    cdef B b = B()
+
+    # A.foo is hidden by B.foo, regardless of signature
+    b.foo(1)
+
+_ERRORS = u"""
+17:9: Call with wrong number of arguments (expected 2, got 1)
+"""
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tests/run/cypclass_hide_override.pyx

+# mode: run
+# tag: cpp, cpp11, pthread
+# cython: experimental_cpp_class_def=True, language_level=2
+
+cdef cypclass A nolock:
+    int a
+
+    __init__(self, int a):
+        self.a = a
+
+    A foo(self, int other):
+        return A(a + other)
+
+cdef cypclass B(A) nolock:
+    int b
+
+    __init__(self, int b):
+        self.b = 10 + b
+
+    B foo(self, int other):
+        return B(b + other)
+
+def test_hide_override():
+    """
+    >>> test_hide_override()
+    21
+    """
+    cdef B b1 = B(0)
+
+    # This should not result in a 'ambiguous overloaded method' compilation error
+    cdef B b2 = b1.foo(1)
+
+    return b2.b
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