Change local rpc

[kuzdogan]

PR to change the primary Ethereum nodes used by Sourcify (Mainnet, Goerli, Sepolia). Instead of the LAN ones we use the ethpandaops' nodes.

Since the authentication is done through Headers, we had to change the rpc field in the sourcify-chains.ts into an ethers.js FetchRequest.

With that I also abstracted away the blockchain connections (getTx, getBytecode etc.) into a class called SourcifyChain inside lib-sourcify, such that we don't need to go through redundantly checking the rpcUrl + creating the JsonRpc or Websocket providers + sequentially trying the providers with the same sequential logic spread out to different places. With this, we have everything wrapped in SourcifyChain methods, and there's no need to create a new Provider every single time.

_{View in Huly HI-546}

[marcocastignoli]

It is now much more readable having the SoucifyChain class. I read the edits multiple times but I cannot find any problem, 💯 again