MIR: Add initial tzts

Context

Adds a couple tzts to be used for initial prototype validation. The issue mentions factorial, but in discussions on slack we also thought that Fibonacci would work well. I figured, why not both.

Closes: #6211 (closed)

Milestone: %(2023Q3) MIR: prototype

Manually testing the MR

Extract the code part of the tzt, add CAR at the beginning, NIL operation; PAIR at the end, and specify parameter nat; storage int;, such that the end result looks like this:

parameter nat;
storage int;
code { CAR; <extracted code>; NIL operation; PAIR };

Run the resulting contract with octez-client --mode mockup --protocol PtNairob run script <tzt file> on storage 0 and input <input>.

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