Proto/Michelson: Normalize lambdas during elaboration

Context

This MR modify the elaboration of lambdas to call the unparse_code_rec function on the Micheline component. The effect is to normalize all lambdas into Optimized mode at elaboration.

A similar normalization was already done at unparsing (hence the name of the normalization function unparse_code_rec) but unfortunately we cannot get rid of it because normalization to Optimized_legacy mode is needed when lambdas are PACKed.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR