Request for PR: Use Foundry Anvil for tests

[tmm]

wagmi runs its test suite against a mainnet fork using Hardhat's Mainnet forking. While this is a boon for development (it allows us to simulate state changes locally or during continuous integration), there are a couple opportunities to improve wagmi's current implementation:

• Support forking multiple networks. Hardhat doesn't support forking multiple networks. It would be great if we could fork and run more than just mainnet to test against other chains and their nuances.
• Run networks in service containers during CI. Currently we run Hardhat and jest in parallel using start-server-and-test. This is slow and causes sporadic timeouts. By running the networks as service containers, we could split the test suite into shards and run in parallel, speeding up test runs significantly.
• Execute tests against Anvil. Foundry is the most popular toolchain for developing Ethereum applications. It would be great to bring this in to power test nodes. Bonus points for creating a guide on how to use wagmi and Anvil together.

The ideal PR would address these points, while making sure it is still easy to setup and run tests in during development.

[tmm]

I'm working on it right now 😅

[tmm]

Done #751