Improve function handling and name resolution in local Python executor

[aremeis]

The following tests for the local Python executor fail and IMHO they should not:

def test__name__():
    code = dedent("""\
        def foo(): return 0
        foo.__name__
        """)
    result, _ = evaluate_python_code(code, {}, {})
    assert result == "foo"

def test_function_returning_function():
    code = dedent("""\
        def f(): 
            return lambda x: x + 1
        f()(1)
        """)
    result, _ = evaluate_python_code(code, {}, {})
    assert result == 2

This PR fixes the issues by:

• Setting __name__ attribute on functions
• Generalising the resolution of function calls