typing: add a fake `__init__()` to bytestr to distract pytype I'm not sure what changed before pytype 09-09-2021 (from 04-15-2021), but these started getting flagged. This wrapping an exception in a `bytestr` pattern has been flagged before, and I've fixed it then with `stringutil.forcebytestr()`. But that doesn't work here, because it would create a circular import. I suspect the issue is `bytes.__new__()` wants `Iterable[int]`, so it just assumes the subclass will also take that. The referenced pytype bug isn't an exact match, but seems related and the suggested workaround helps. The specific warnings fixed are: File "/mnt/c/Users/Matt/hg/mercurial/encoding.py", line 212, in tolocal: Function bytestr.__init__ was called with the wrong arguments [wrong-arg-types] Expected: (self, ints: Iterable[int]) Actually passed: (self, ints: LookupError) Attributes of protocol Iterable[int] are not implemented on LookupError: __iter__ Called from (traceback): line 353, in current file File "/mnt/c/Users/Matt/hg/mercurial/encoding.py", line 240, in fromlocal: Function bytestr.__init__ was called with the wrong arguments [wrong-arg-types] Expected: (self, ints: Iterable[int]) Actually passed: (self, ints: UnicodeDecodeError) Attributes of protocol Iterable[int] are not implemented on UnicodeDecodeError: __iter__ Differential Revision: https://phab.mercurial-scm.org/D11466