Return prover key checkpoint information programmatically.
See checkpoint-list for relevant background and related
utilities. Here we explain only how checkpoint-info-list differs from
checkpoint-list. The difference is that instead of a list of clauses,
it returns a list of alists each of the following form.
((:clause-id . clause-id)
(:clause . clause)
(:pushed . pushed))
Here, clause-id is the clause-identifier of the indicated
clause. The value of pushed is left undocumented here (low-level
technical note: it comes from the :pushed field of the corresponding