Ledger state is translated repeatedly across hard fork point

Suppose we have seen the last Byron block, and are about to transition to Shelley. At every slot (i.e., every second) every node will determine if they are a leader. In order to do that check, they will tick the ledger state. Since we are precisely at the transition point, this tick will mean translation the entire ledger state. The result of this ticked ledger state is thrown away, whether or not a block was produced, and _if_ a block was produced, then the ledger state is ticked once more when that block is added to the chain DB and validated. This means that every node will translate the ledger state time and again until it receives or produces the first block after the transition. Fortunately, the overlay schedule means that this block will be produced immediately in the first slot after the transition, so this shouldn't cause much hassle.

We could improve the situation by only ticking the ledger _view_ (aka, forecasting). This is significantly cheaper.