refactor(app): Extract bootstrap and validators modules from app.rs

[mpoke]

Summary

• Extract node initialization logic (genesis and existing block recovery) into new bootstrap.rs module
• Extract validator contract interaction and parsing logic into new validators.rs module with unit tests
• Reduce app.rs by ~270 lines, improving code organization and testability

[rnbguy]

Thanks for the cleanup ! 🙏🏼

ps. fix the clippy lint.

[rnbguy]

LGTM 🎉