Update Chai to version 6

### Describe the issue

Update [Chai to version 6](https://www.npmjs.com/package/chai/v/latest) in all packages, including the [hardhat-toolbox-mocha-ethers](https://github.com/NomicFoundation/hardhat/tree/main/v-next/hardhat-toolbox-mocha-ethers), both dependencies, peer dependencies and dev dependencies.
Run all available tests and verify the functionality manually.