[cr133][rust] Fix unused imports in brave code

This warning is now enabled for all chromium code, and it has been
triggered with some of the zcash code.

Additionally, this change has to correct a lot of the formatting for
that file, which seems to have changed considerably.

Chromium change:
https://chromium.googlesource.com/chromium/src/+/6f81efe9a3d000dcbc952d6f14284c8178a960ec

commit 6f81efe9a3d000dcbc952d6f14284c8178a960ec
Author: Lukasz Anforowicz <lukasza@chromium.org>
Date:   Thu Jan 2 13:45:03 2025 -0800

    Stop globally disabling `unused-imports` lint when compiling Rust.

    rust-lang/rust#121708 (comment)
    points out that new linting scenarios have been moved into a separate
    lint.  Thanks to this, we no longer need to globally disable this lint
    in Chromium (some narrower exclusions still need to apply).

    Bug: chromium:326247202

Author: cdesouza-chromium