interfaces: add the missing `self` arg to the dirstate Protocol class This clears all of the errors that PyCharm has been flagging in this file, since the zope interface was declared here.

interfaces: convert the dirstate zope interface to a Protocol class This is a small trial run for converting the repository interfaces enmasse, in the same series of steps. I'm not sure that this current code is valid (it has zope attribute fields, and it's missing all of the `self` args on its functions, but that was the previous state of things, and made PyCharm really unhappy). But it will be easier to review the repository interface changes if this change is separate from adding `self` and dropping the zope attributes all over. Having an empty constructor in a protocol is weird. I'm not sure if these args should be converted to fields that all subclasses would have, and comments around existing attributes say some should be going away. Comment it out for now so that it's not in the way, but also not forgotten.

tests: disable `test-check-interfaces.py` while converting to protocols The goal is to convert everything, so get it all out of the way. The interfaces don't get that much maintenance that this needs to be tested right now.

tests: always access the mercurial repo through `helpers-testrepo.sh` In some contexts the mercurial repo needs to be accessed through system hg. That's what `helpers-testrepo.sh` enforces, but some tests incorrectly use the mercurial repo without going through that script. This patch fixes those tests.

tests: in helpers-testrepo.sh switch from shell aliases to functions The reason is that I want this script to work in non-interactive shells too. (will be used in the next commit)

rust: fix the deprecation warning in NaiveDateTime::from_timestamp This warning appears between chrono 0.4.34 and 0.4.38, so isn't affecting the current lock file, but it would come when we upgraded the version.

run-tests: ensure that --no-rust do not use rust Since having a valid value in HGWITHRUSTEXT is enough to trigger the use of rust, we need to unset it before install to be sure.