Simplify iteration idioms (#13834)

Remove unnecessary uses of `.as_ref()`, `.iter()`, `&**` and similar, mostly in situations when iterating over variables. Many of these changes are only possible following #13826, when we bumped our MSRV to 1.80: several useful implementations on `&Box<[T]>` were only stabilised in Rust 1.80. Some of these changes we could have done earlier, however.

crates/ruff_python_formatter/src/pattern/pattern_arguments.rs

@@ -48,7 +48,7 @@ impl FormatNodeRule<PatternArguments> for FormatPatternArguments {
                                 pattern.format().with_options(Parentheses::Preserve),
                             )
                         }))
-                        .nodes(item.keywords.iter());
+                        .nodes(&item.keywords);
                 }
             }