refactor: apply clippy::needless_borrow

[shulaoda]

Summary

• Removes 12 redundant & borrows where the callee already takes a reference, across src/chains.rs, src/expr.rs, src/format_report_formatter.rs, src/items.rs, src/macros.rs, src/overflow.rs, src/sort.rs, and src/types.rs.
• Addresses clippy::needless_borrow, run as a single-rule pass: cargo clippy -- -A clippy::all -W clippy::needless_borrow.

Representative changes:

• rewrite_paren(context, &expr, …) → rewrite_paren(context, expr, …)
• rewrite_call(context, &callee_str, &args, …) → … , args, …
• rewrite_where_clause(context, &after_where_clause, …) → … , after_where_clause, …
• rewrite_generics(context, …, &fn_sig.generics, …) → … , fn_sig.generics, …
• maybe_get_args_offset(…, &self.context.config) → … , self.context.config
• ca.cmp(&cb) → ca.cmp(cb) (and similar)
• first_line_width(&pred_str) → first_line_width(pred_str)

In every case the argument was already an &T, so the extra & was reborrowed to the same type — no observable change.

[ytmimi]

Going to close until we decide on which clippy lints we want to enforce in the codebase.