Write PIDController.t.sol tests

[steve0xp]

Primary Goals of PR

Write tests for PIDController.sol in PIDController.t.sol:

1. Write tests for PIDController.sol using foundry
2. Adjust contracts if needed (small tweaks)

NOTES:

• Pools contracts code was copied over from commit on Niv's branch here in order to run tests btw EUSDPools and PIDController.sol
  • Pool.sol will be deleted once draft PR is complete (after PR Review and Pools associated tests are checked through).
  • Test code associated to Pool.sol will be commented out. Then coordination will be required between Pools PR and this one.
  • Once Niv's Pools code and tests are merged to main, proper rebasing and coordination will be done wrt those files.
• I actually think that SHARE aspects (share address setter, share price && eusd price) ought to be within the actual erc20 contract itself. Our stablecoin is fractional and it would be good to pair the associated other ERC20 token with it. I guess there is no standard for fractional stablecoins eh?
  • That said, we could have it in a separate contract too, or leave it here. I'll leave it in PIDController files for now, but can move it based on people's thoughts.

[steve0xp]

@davekaj Changes have been made, and responses given on some of the change requests you outlined. Please review at your leisure and once we are good with this PR then I can remove the Pool.sol and comment out the associated test code while we coordinate the merging of Niv's Pool PR #6

[steve0xp]

Changes have been made, and comments acknowledged.