[`perflint`] Clarify that `PERF402` applies to any iterable (#26242)
First contribution here, hi! Picking up #21593 as a small intro PR.
PERF402's current "What it does" says it catches copies of an "existing
list", but the rule also fires whenever a `for` loop appends every item
of any iterable to a list while the source isn't required to be a list
(only the destination is). The issue reporter pointed this out and
suggested wording closer to "for loops that can be replaced with
`list()`", which is what I went with here.
Scope is intentionally tiny: just the `## What it does` and `## Why is
this bad?` doc comments. Violation message, example, rule logic, and
tests are unchanged so no snapshots move.
Closes #21593.
ruff
aa96a05d - [`perflint`] Clarify that `PERF402` applies to any iterable (#26242)
