rust: clean Rust 1.88.0's `clippy::uninlined_format_args` lint

rust: clean Rust 1.88.0's `clippy::uninlined_format_args` lint

Starting with Rust 1.88.0 (expected 2025-06-26) [1], `rustc` may move
back the `uninlined_format_args` to `style` from `pedantic` (it was
there waiting for rust-analyzer suppotr), and thus we will start to see
lints like:

    warning: variables can be used directly in the `format!` string
       --> rust/macros/kunit.rs:105:37
        |
    105 |         let kunit_wrapper_fn_name = format!("kunit_rust_wrapper_{}", test);
        |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args
    help: change this to
        |
    105 -         let kunit_wrapper_fn_name = format!("kunit_rust_wrapper_{}", test);
    105 +         let kunit_wrapper_fn_name = format!("kunit_rust_wrapper_{test}");

There is even a case that is a pure removal:

    warning: variables can be used directly in the `format!` string
      --> rust/macros/module.rs:51:13
       |
    51 |             format!("{field}={content}\0", field = field, content = content)
       |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args
    help: change this to
       |
    51 -             format!("{field}={content}\0", field = field, content = content)
    51 +             format!("{field}={content}\0")

The lints all seem like nice cleanups, thus just apply them.

We may want to disable `allow-mixed-uninlined-format-args` in the future.

Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
Link: https://github.com/rust-lang/rust-clippy/pull/14160
Acked-by: Benno Lossin <lossin@kernel.org>
Reviewed-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250502140237.1659624-6-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>