refactor(clearnode): migrate Signature{r,s,v} to []byte

[nksazonov]

• rebase on base after refactor(contract): migrate sig to bytes #279 is merged

[gemini-code-assist]

Summary of Changes

Hello @nksazonov, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant refactoring effort to standardize the representation of cryptographic signatures throughout the project. By migrating from a custom Signature struct to a raw bytes array, the codebase achieves greater consistency between the Go client and Solidity contracts. This change simplifies signature handling, reduces boilerplate code, and aligns the project with common Ethereum signature formats, ultimately improving maintainability and clarity.

Highlights

• Go Client Simplification: The Go Signer and nitrolite.Sign functions have been refactored to directly return []byte signatures, eliminating the need for intermediate struct conversions. The NitroSign helper function has also been removed, consolidating signature generation logic.
• Solidity Contract Alignment: All relevant Solidity contracts and interfaces, including Custody.sol, Utils.sol, IChannel.sol, Types.sol, and various adjudicators, have been updated to use bytes for signature parameters and storage. This ensures consistency with the Go implementation and streamlines signature verification on-chain.
• Test Suite Adaptation: The comprehensive test suites for both Go and Solidity have been updated to reflect the new bytes signature type, ensuring that all signing and verification logic remains correct and robust after the refactoring.

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[gemini-code-assist]

Code Review

This pull request refactors the signature representation from structs to byte slices across the codebase, enhancing code clarity and maintainability by simplifying signature handling logic and removing redundant conversions.