Feat: Add Multisig Payment Channel Support

[pali101]

Features

• Implemented Multisig_2of2.sol with support for native and ERC20 payment channels.
• Added core functions: createChannel, redeemChannel, and reclaimChannel.

Tests

• Added base test helpers to streamline multisig test setup.
• Comprehensive test coverage for createChannel, redeemChannel, and reclaimChannel logic.

Chores

• Updated Solidity version across contracts and scripts to ^0.8.28.
• Updated foundry.toml with new solc version (0.8.30) and formatting fixes.

[Copilot]

Pull Request Overview

This PR introduces 2-of-2 multisig payment channel support, including native and ERC20 channels, along with comprehensive tests and tooling updates.

• Implements Multisig_2of2.sol with createChannel, redeemChannel, and reclaimChannel functions.
• Adds end-to-end tests in test/multisig for channel creation, redemption, and reclamation.
• Updates Solidity pragmas to ^0.8.28 and bumps the Foundry compiler to 0.8.30.

Reviewed Changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Multisig_2of2.sol	Core multisig payment channel contract implementation
foundry.toml	Bumped solc version to 0.8.30
test/multisig/CreateChannel.t.sol	Tests for createChannel behavior
test/multisig/RedeemChannel.t.sol	Tests for redeemChannel scenarios
test/multisig/ReclaimChannel.t.sol	Tests for reclaimChannel logic
test/VerifyHashchain.t.sol	Pragma change and test modifier update

Comments suppressed due to low confidence (6)

src/Multisig_2of2.sol:24

• [nitpick] Typo in identifier: lastNounce should be lastNonce to match common terminology and improve readability.

        uint256 lastNounce; // Last used nonce to prevent replay attacks and ensure order

test/multisig/RedeemChannel.t.sol:109

• Test function name has an extra s prefix (testsMultisig...) and won't be discovered by Forge; rename to testMultisigCannotRedeemWithIncorrectAmountHigher.

    function testsMultisigCannotRedeemWithIncorrectAmountHigher() public {

test/multisig/ReclaimChannel.t.sol:78

• [nitpick] In _assertChannelStateWhenFailedReclaim, the parameter payeeBalanceBefore actually refers to the payer's balance; consider renaming to payerBalanceBefore for clarity.

        uint256 payeeBalanceBefore,

src/Multisig_2of2.sol:92

• Solidity's require only accepts a string error message. To use a custom error, replace this require with an if check and revert ReclaimAfterMustBeAfterExpiration(...).

        );

test/VerifyHashchain.t.sol:36

• Adding the view modifier to a test function can prevent state modifications Forge expects; remove view so the test is executed normally.

    function testInvalidHashchainWrongDepth() public view {

foundry.toml:5

• Configuration parsing typically expects a space around the = (i.e., solc = "0.8.30"). Without spaces, Foundry may fail to read this setting.

solc="0.8.30"