Document that std::hash::Hasher::finish() does not reset the hasher.

[partim]

Clarifies the fact that finish() doesn’t in fact end or reset the hasher. This was surprising to me …

Follows up on and fixes #43763

[rust-highfive]

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[steveklabnik]

@rust-lang/libs I want to make sure this is a feature, not a bug. These docs look good to me, so as long as yinz sign off on it, r=me

[alexcrichton]

IIRC this was the intention, yes. Thanks for the PR @partim!

[partim]

As @bluss pointed out in #43763, because of the &self, the method can’t really do anything else.

[steveklabnik]

@bors: r+ rollup

great, thank you!

[bors]

📌 Commit 02aaa11 has been approved by steveklabnik