AthenaDataset._is_valid() is extremely brittle

[neutrinoceros]

Bug report

Bug summary

AthenaDataset._is_valid() is currently implemented as

    @classmethod
    def _is_valid(self, *args, **kwargs):
        try:
            if "vtk" in args[0]:
                return True
        except Exception:
            pass
        return False

Note that the try/except block is basically useless and that the whole function is equivalent to

    @classmethod
    def _is_valid(self, *args, **kwargs):
        return "vtk" in args[0]

This is a problem for two reasons:

• it can easily (however unlikely) lead to random YTAmbiguousDataType, as it happened in refactor: remove yt.funcs.ensure_tuple #3000
• it strongly limits the design space for other frontends targeting vtk files

I have no expertise with Athena so I'm not in a position where I can easily come up with a more robust validation function.