WIP: Add Scribble properties to the codebase

[JoranHonig]

Hey Everyone,

In this pull request, I've added several properties to the codebase.

This is still a work in progress; however, I've opened this pull request to discuss the properties as they are now.

In a follow up PR, I'll add a configuration for setting up a fuzzing campaign 👍 .

Testability

There are some parts of the codebase where the structure is not optimal for testing.

An example is the _executeDonationSwaps function in the RoundManager. This function implements both logic to loop over the swaps and to execute swaps. It is possible to consider extracting the logic for executing a single swap into a separate function, which would allow you to write properties & tests for this code in isolation.

For example, take the following property, which ensures that you get the minimum amount out of the swap.

  ///#if_succeeds 
  /// let outToken = IERC20(swap.path.toAddress(swap.path.length - 20)) in
  /// old(outToken.balanceOf(address(this))) + swap.minOutAmount == outToken.balanceOf(address(this));
  function executeDonationSwap(SwapSummary swap, uint256 _deadline) internal {
   ...
  }

[thelostone-mc]

@JoranHonig could you drop in the scribble doc / reading material as well for folks to checkout and get a better sense of the PR ?