Throttle Alchemy RPC requests in case of rate limiting

[agostbiro]

Alchemy guarantees a certain throughput, but allows higher if they have free capacity. This means that it doesn’t make sense to proactively apply throttling, instead it needs to be applied when getting rate limited.

Definition of Done

When running Hardhat provider integration tests with Alchemy, the backoff in case of rate limiting takes into account the compute capacity units of the user.