chore: cargo fmtの適用とCI（build/clippy/fmt）の追加

[suzuki-toshihir0]

Summary

• cargo fmt の適用（コードスタイルの統一）
• CI に以下のジョブを追加
  • Build: cargo build
  • Clippy: cargo clippy -- -D warnings
  • Format: cargo fmt --check

Test plan

• CI の各ジョブ（test/build/clippy/fmt）が全て通ることを確認

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR applies automatic code formatting via cargo fmt to ensure consistent code style across the codebase and enhances the CI pipeline by adding three new jobs: Build, Clippy (linting), and Format checking. These additions strengthen the quality assurance process by catching build failures, lint warnings, and formatting inconsistencies early.

Changes:

• Applied cargo fmt to format Rust source files according to standard conventions
• Added Build job to verify the project compiles successfully
• Added Clippy job to enforce lint-free code with warnings treated as errors
• Added Format job to ensure all code adheres to standard Rust formatting

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

File	Description
tests/integration_test.rs	Reformatted multi-line assert macro for better readability
src/formatter.rs	Split long method chain across multiple lines per Rust formatting conventions
src/config.rs	Reformatted method chains and removed trailing whitespace at end of file
.github/workflows/ci.yml	Added three new CI jobs (build, clippy, fmt) to enhance quality checks

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