Replace delta view with spockState and storageState

Changes relative to delta view:
- encode operation type as part of spock hash.  This prevents operation
  substitution / omission.  In particular, the original implementation
  generate identical hashes for:
    1. Get(registerId) and Set(registerId, "")
    2. with vs without DropChanges()
- encode register id / value length as part of spock hash to guard against
  string injection attack
- the spock mutex in delta view is no longer needed.  Result collector
  refactoring + explicit finalized execution snapshots eliminated the
  accidential data race.
- spockState is no longer accessible once Finalize is called.  We can't safely
  support mutation after Finalize since the SumHash is not idempotent.
- storageState keeps track of the read (from the underlying storage) set rather
  than the touch set.  Note that the touch set can be constructed from the read
  and write sets (e.g., execution snapshot's AllRegisterIDs), but not vice
  versa.

Author: pattyshack