Unity 4.20.0 - MetaMask SDK Improvements

- [Native] Upgrade MetaMask SDK to 2.1.0 by @ecp4224 in https://github.com/thirdweb-dev/unity-sdk/pull/207
- Utilizes MetaMask's new ConnectWith functionality to connect and switch to the right network within a single call.
- Improves network switching behavior and handled errors better.
- Fixes errors encountered when switching to a MetaMask default chain such as Sepolia.
- Refactored internal code to use new MetaMaskSDK APIs.
- [Cross-Platform] Added support for new chains.
Release: https://github.com/thirdweb-dev/unity-sdk/releases/tag/v4.20.0