pytype: work around wrong ImportError flagging As documented in https://github.com/google/pytype/issues/163, newer versions of Pytype do not understand caught `ImportError`, so we temporarily ignore them where applicable.

zeroconf: fix boolean return value This was (wrongly) flagged by Pytype as being undefined since it doesn't seem to understand `try` blocks. However, the caller is expecting a boolean and the fix to appease Pytype is simple, so we do both.

convert: fix various leaked file descriptors Some of these only leaked if an exception occurred between the open and close, but a lot of these leaked unconditionally. A type hint is added to `parsesplicemap` because otherwise this change caused pytype to change the return type from this to `Dict[nothing, nothing]`.

convert: stringify `shlex` class argument The documentation is handwavy, but typeshed says this should be `str`[1]. I'm not sure if this is the correct encoding (vs `fsencode` or "latin1" like the tokens returned by the proxy class). While we're here, we can add a few more type hints that would have caused pytype to flag the problem. [1] https://github.com/python/typeshed/blob/6a9b53e719a139c2d6b41cf265ed0990cf438192/stdlib/shlex.pyi#L51

typing: add trivial type hints to the convert extension's common modules This started as ensuring that the `encoding` and `orig_encoding` attributes has a type other than `Any`, so pytype can catch problems where it needs to be str for stdlib encoding and decoding. It turns out that adding the hint in `mercurial.encoding` is what was needed, but I picked a bunch of low hanging fruit while here. There's definitely more to do, and I see a problem where `shlex.shlex` is being fed bytes instead of str, but there are not enough type hints yet to make pytype notice.

convert: drop a duplicate implementation of `dateutil.makedate()` I noticed this because the signature generated by pytype recently changed to be less specific. When the method was introduced back in 337d728e644f, `util.makedate()` didn't take an optional timestamp arg. But now it does, and the methods are the same (except the `dateutil` version validates that the timestamp isn't a negative value). I left the old method in place in case anyone has custom convert code that monkey patches it.