Companion for substrate#12530: Consolidate and deduplicate MMR API me…

…thods (paritytech#6167)

* histor. batch proof: make best block arg optional

* make generate_batch_proof stub for historical

* merge generate_{historical_}batch_proof functions

* merge generate_{batch_}proof functions

* merge verify_{batch_}proof functions

* merge verify_{batch_}proof_stateless functions

* rename BatchProof->Proof

* update lockfile for {"substrate"}

Co-authored-by: parity-processbot <>