csp.Struct doesnt support property setters

At the moment looks like csp.Struct wont properly process setattr calls when setting via a property, it wouild be very useful to get this to work.

Sample repro:

class S(csp.Struct):
    _a : int

    @property
    def a(self):
        return self._a

    @a.setter
    def a(self, x):
        self._a = x

s = S()
s.a = 1
Traceback (most recent call last):
  File "/home/ra7293/pycharm-community-2023.1.2/plugins/python-ce/helpers/pydev/pydevconsole.py", line 364, in runcode
    coro = func()
  File "<input>", line 1, in <module>
AttributeError: PyStruct.cpp:setattr:432:AttributeError: 'S' object has no attribute 'a'

Run the Python reproduction first, then trace csp.Struct attribute handling into the PyStruct.cpp:setattr path named in the traceback. Check how property setters are recognized and add or update focused coverage if the repository has relevant tests; done means assigning s.a invokes the setter without the AttributeError.