Conan 2 arbitrary command output stream capture interfering with message passing

[markfinal]

In the arbitrary command testing in Conan 2, I cannot see the stderr output from Conan.

This is because of the patching in _patch_conan_output_initialiser

    from conan.api.output import ConanOutput

    conanoutput_old_init = ConanOutput.__init__

    def new_init(self: ConanOutput, scope: str = "") -> None:
        conanoutput_old_init(self, scope)
        self.stream = QueuedStreamSix(queue, Stdout)

    ConanOutput.__init__ = new_init

The code in src/cruizlib/workers/api/v2/arbitrary.py replaces the standard streams

        temp_out = StringIO()
        temp_err = StringIO()
        sys.stdout = temp_out
        sys.stderr = temp_err

but then the _patch_conan_output_initialiser replaces it again. So we never get to see it.

The long and short of this is that the tests cannot check expected message outputs in failure cases.