Proto: Tickets lazy storage diff

Context

It's the sixths of a series of MRs for introducing a ticket accounting feature in the protocol as described in this document.

See the milestone for a break down of the work.

This MR introduces a module Ticket_lazy_storage_diff which exposes a single-function entry point for applying ticket accounting post script execution:

val ticket_diffs_of_lazy_storage_diff :
  Alpha_context.context ->
  Alpha_context.Lazy_storage.diffs_item list ->
  ((Ticket_token.ex_token * Z.t) list * Alpha_context.context) tzresult Lwt.t

Manually testing the MR

Run tests with:

> dune exec src/proto_alpha/lib_protocol/test/main.exe -- test "^ticket lazy storage"

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, the Development Version section of CHANGES.md for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR