chore: add rustfmt.toml and clippy.toml for consistent code style

## Motivation

No formatter or linter configuration exists. Different contributors will inevitably format code differently without a shared config.

## Proposal

- Add `rustfmt.toml` with settings like `max_width = 100`, `edition = "2021"`, etc.
- Add `clippy.toml` to configure any project-specific lints (e.g. `too-many-arguments-threshold`)
- Optionally add a `[lints]` section to `Cargo.toml` to enforce `clippy::pedantic` or selected lints at the workspace level

This pairs well with the CI workflow (#2) — once we have fmt and clippy configs, CI can enforce them automaticaly.

Start by inspecting Cargo.toml and the existing project layout, then check whether rustfmt.toml, clippy.toml, or a CI workflow already exists. Done means adding the agreed formatter and linter configuration, optionally wiring selected lints in Cargo.toml, and confirming the configuration is compatible with the project.

Written by the indexing model from the issue text.