Bump Rust toolchain to 1.97.1

[perryqh]

• Moves the pinned toolchain from 1.92.0 to 1.97.1, the current stable release.
• No CI workflow pins a Rust version, so all four workflows pick this up from rust-toolchain.toml automatically. The release workflow is cargo-dist-generated and installs via rustup, so it inherits it too.

Why there are source changes

• Rust 1.97's clippy flags a redundant & passed to format-like macros, which 1.92's did not. Under CI's RUSTFLAGS=-Dwarnings these 9 warnings fail the Lints job, so the bump can't land without fixing them.
• All 8 source/test changes are the same one-character edit: format!("{}", &x) becomes format!("{}", x). Display and Debug forward transparently through references, so formatted output is byte-identical and no behavior changes.

Reviewing this

• 565183b is entirely mechanical, safe to skim.
• 6e25d06 is the one substantive line.
• The lint fixes land first so each commit passes clippy on its own (verified clean under both 1.90 and 1.97), meaning git bisect never lands on a red commit.

Contributor impact

• Local builds now need 1.97.1; rustup installs it automatically from rust-toolchain.toml.
• No rust-version/MSRV is declared in Cargo.toml, so no downstream compatibility constraint is affected.

Heads-up: unrelated flaky test

While running the suite locally, test_respect_gitignore_can_be_disabled failed once under full concurrent load, then passed in isolation. This looks like a pre-existing test-isolation bug rather than something introduced here:

• test_respects_global_gitignore mutates the developer's real global git config (git config --global core.excludesFile) and is marked #[serial].
• serial_test's #[serial] only serializes against other #[serial] tests, not against unmarked parallel ones, so test_respect_gitignore_can_be_disabled can run while excludesFile is mid-set/unset and pick up a bogus ignore path.
• This PR touches no gitignore or zeitwerk code, only format arguments.

If CI goes red on that test, this is the likely cause. Worth fixing separately.

Related: a failed local run can leave tests/fixtures/app_with_unnecessary_dependencies/packs/foo/package.yml modified, since test_auto_correct_unnecessary_dependencies rewrites it and skips cleanup when the suite aborts.

Follow-ups noted, deliberately not included

• parse_utils.rs:149-152 is if name.is_some() { name.unwrap_or_else(|| panic!(...)) }. The panic is unreachable given the guard and wants to be if let Some(..) = name. There is also a stale commented-out copy just above it that still contains the old &node, so it will drift further out of sync.
• ci.yml uses actions/checkout@v2 (deprecated Node runtime) and audit.yml uses the archived actions-rs/audit-check@v1.

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