Separate L1 and L2 while syncing

[joshklop]

The Problem Right now, we sync state from L1 and blocks/transactions/etc. from L2 in the same logic. This makes for an enormous Synchronizer object that encapsulates a myriad of unrelated dependencies. Cleanly separating L1 and L2 should make the sync process more modular.

Possible Solution Move the logic for L1 and L2 to separate packages, probably internal/sync/l1 and internal/sync/l2.