Replaced the ForkToBlockNumber array with a (more complicated) object called ForkTransitionTable that knows the difference between block-based forks, time-based forks, and the special cases like MergeFork and Shanghai (which IIUC needs to be doable via either block number or time, at least temporarily).

Created a type called ForkDeterminationInfo to represent the information needed to determine which hard fork a particular block is on. In the past all we needed was a block number; now we need to pass in both a block number and timestamp (and if mergeForkBlock isn't specified, maybe TD as well), so I created a type for it (though I don't love the name).

Several things are still unresolved. (See various places that say FIXME-Adam.) But I think this is progress.

Intending to implement the V2 versions next. (I need the bodies to be
in separate procs so that multiple versions can use them.)

(We only use the new forkTransitionTable now.)

…-forking