Reduce flakiness of Solidity tests depending on Alchemy

[nebasuke]

Context: https://github.com/NomicFoundation/edr/pull/1012

Consider Agost's suggestions:

• It looks like there is a proxy server option for self-hosted runners (which we are using for the benchmark): https://docs.github.com/en/actions/how-tos/managing-self-hosted-runners/using-a-proxy-server-with-self-hosted-runners#configuring-a-proxy-server-using-environment-variables
• But maybe the simplest solution would be to use a local Ethereum node in fork mode instead of Alchemy.

This should be done as a low-effort as (per Agost:) mid-term, the unreliability of StdUtilsForkTest would be solved by merging the EDR and Foundry fork implementations, as EDR caches fork initialization more aggressively. If using a known RPC provider and a pinned block number, EDR won't make any network requests to initialize a fork, while Foundry will fetch the chain id and latest block number every time iirc.