Use block number / information to determine fork rules

[arnetheduck]

In code like

nimbus-eth1/nimbus/core/withdrawals.nim

Line 25 in 4e50b05

if com.forkGTE(Shanghai):

, the global com state is used to validate data found in the block itself - this is confusing - the block rules should be decided from the given block header since there may be a mismatch between the two.