chore: remove nightly format config

[estensen]

make lint doesn't use nightly Rust and is just noise

Run make lint
cargo fmt -- --check
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
...

https://github.com/flashbots/rbuilder/actions/runs/17913195731/job/50929259682?pr=717

Alternatively use nightly as referenced in

rbuilder/CONTRIBUTING.md

Line 38 in d1cdaf6

Follow the [Rust Style Guide](https://doc.rust-lang.org/nightly/style-guide/) recommendations.

[Copilot]

Pull Request Overview

This PR removes the nightly Rust formatting configuration to eliminate warnings during linting. The change removes a rustfmt configuration option that requires nightly Rust features, which was causing noise in the CI pipeline when using stable Rust.

• Removes imports_granularity = "Crate" configuration that requires nightly Rust
• Keeps reorder_imports = true which works with stable Rust
• Eliminates warning messages during make lint execution

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