Utilize the reader monad in sbv to season the solver

[doyougnu]

  With the parallel version of vsmt we have to season the solver with the
  variational core. This means that we actually compute ~n~ ~IL~'s where ~n~
  is the number of threads. This is likely a small price to pay for the
  parallelism but could certainly be reduced. SBVs ~SymbolicT~ is a reader
  monad over ~IO~ but sbv doesn't export the ~ReaderT~ type class instance,
  so in the main thread we can season, then grab the state with
  ~T.symbolicEnv~ but then there is no way for me to call ~local~ over the
  thread instances and thus no way to replace the thread states with the
  seasoned state. Hence, we are forced recompute the state for each thread
  with a call with ~toIL~.

[doyougnu]

Note that we could season the solver for every recursive call, that is:

• You start solving
• generate a variational core
• capture solver state
• season threads with solver state
• when a new choice is found, each alternative will be tried
• this means that the new vpl formulas, which represent each alternative's variant, will introduce new non-variational terms that were previously blocked by the choice
• thus we generate a new variational core for each alternative
• then at this point we can capture the solver state, and re-season whichever thread receives the request to process that alternative
• hence we'd save time calculating the new variational core for any subsequent recursive calls which would result from finding new un-seen choices in the recursive call