feat: add rustfmt.toml

[onbjerg]

Introduces the same rustfmt settings as we use in Foundry, Reth, and Alloy, and formats the code.

This config features some nice things like comment formatting, import "merging", and import reodering.

[sslivkoff]

cherry-picked your 8082372 commit into 8dc8361 due to branch divergence

thanks for the pr. glad to adopt as much of foundry's tooling config as possible