Revist Celo detection

[leoyvens]

#2670 introduced logic that checks the chain_id to see if it is Celo, and in that case it sets the reorg threshold to zero. But we would like to change how that is done. It is currently implemented inefficiently because the call is done every time a block stream is constructed, instead of once per provider, so that can be optimized. Another consideration is that it would be generally useful to have a per-provider configuration of the reorg threshold, in which case the necessity of any chain id based detection is questionable.