fix: clippy lints across lib and test targets

[N4M3Z]

Problem

CI fails on every PR: the runners' Rust 1.97 clippy added question_mark (fires in src/yaml/mod.rs) and stricter format lints in test targets, all denied under -D warnings. forge-cli#84 is red through no fault of its diff.

Fix

Apply the machine-suggested rewrites: ? instead of the match in the yaml path walker, string literals instead of argument-less format!, inlined format args, and a method reference instead of a redundant closure. No behavior change.

Test plan

• cargo clippy --all-targets -- -D warnings clean
• cargo test green (478 tests)
• cargo fmt applied, prek gate green, tree secret scan clean

[N4M3Z]

Superseded: every lint fixed here has landed on main via #86's precursors and #87. Rebasing onto main leaves an empty diff.