Add a new kind of benchmark to evaluate Michelson typechecker and interpreter on a corpus

This MR introduces CORPUS_alpha, a new family of benchmark to evaluate Michelson typechecker and interpreter on a corpus.

A corpus is a list of scenarios. A scenario defines a context and a sequence of calls to contracts. The module Scenario offers a syntax and a semantic for these objects.

To implement this feature, we need a (minor) extension of the protocol interface to be able to call the typechecker on a (strict) Micheline node. The previous API only provides typechecking functions working on lazy nodes (that still have to be decoded).