feat: add manual_max and manual_min lints

[sylvestre]

Add two complexity lints that detect a single-sided clamp written as an if/else (or a guarding if) and suggest Ord::max / Ord::min:

let _ = if a < b { b } else { a };  // -> a.max(b)
if cores < b { cores = b; }         // -> cores = cores.max(b);

This is the sound, generalizable form of the manual clamp simplified by hand in uutils/coreutils#12753 (nproc). Unlike manual_clamp, which only fires when both a lower and an upper bound are applied, these catch the common single-bound floor/ceiling case.

Restricted to Ord types so float NaN semantics are not changed, and emitted as MaybeIncorrect since the branching form re-evaluates the selected operand.

changelog: add manual_max and manual_min lints

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[github-actions]

Lintcheck changes for 1dd053a

Lint	Added	Removed	Changed
clippy::manual_max	17	0	0
clippy::manual_min	8	0	0

This comment will be updated if you push new changes

[oech3]

nproc did not compare cores - limit with 1. So this is slightly different with this lint.

[samueltardieu]

You'll have to guard this with a MSRV check (1.21).

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

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  • 1dd053a

[sylvestre]

@samueltardieu done, merci!