Make 'isort' consistent about 'build'

[sirosen]

This does not seem to reproduce consistently -- isort is executing
correctly in pre-commit.ci -- but in some environments and
invocations, isort is incorrectly reordering imports of build
because it gets confused by the piptools.build module.

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• Included tests for the changes.
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[WhyNotHugo]

We could also just use ruff for managing imports. See: #1886

[WhyNotHugo]

(it's probably best to merge this as a short-term fix anyway)

[webknjaz]

I agree that we should slowly adopt ruff.
I'd like to have a separate config, though. But that's a separate thing. I also have some prior art of doing said adoption in stages in Cheroot.

[sirosen]

I wouldn't mind using ruff, although I have been perfectly happy with the tooling which predates it.
I'm not in a hurry about it though.

Right now the major thing I see in pre-commit that needs attention is the mypy configuration. It doesn't even belong in pre-commit (I have some strong opinions on this one), so fixing that will be a body of work in its own right.