Speculative evaluation can cause a large increase in allocations

We've found that for cardano-node speculative evaluation introduced in the coreprep stage can cause a large increase in allocations. Some dictionaries get created a lot more because of this transformation.

I have a draft MR that allows speculative evaluation to be turned off (or turned off for DFun) !13556 (merged) . Perhaps we can change the flag for DFun to one that sets an upper bound on the amount of allocation we do.

Speculative execution was added in: #19224 (closed) / !4833 (closed)