PBT Tests

[bugarela]

We don't have any setup for property-based testing. Pointed out by @shonfeder at https://github.com/informalsystems/tnt/pull/81/files#r853271142. I can see that helping a lot with testing since writing unit tests for individual IR components is already too much - testing combinations of them is unfeasible without PBT.

[shonfeder]

This might be a useful and easy place for me to begin contributing work. Some first steps would include:

• Identify feasible PBT libraries
• Select a library to use
• Write generators for atomic values
• Write generators for compound values
• Write generators for types
• Come up with a list of places where PBTs could be especially useful

[shonfeder]

We talked at the end of last year about having some PBT over our IR might turn up edge cases, which, currently, are left for users to discover :)