Made some safe Gas and Test optimization to Dai contract

[Chijulybuilds]

Securely Saving MakerDAO(Dai) ~~$95_000 yearly!

Gas and Test optimization that saves the protocol

Timestamp: 1782252480 (Tue/June/2026-10:29PM WAT)

Master branch Dai Contract Deployment Gas: 1,851,353 gas
Gas_and_Test_optimization Branch Deployment Gas: 1,429,297 gas

Master branch Dai Contract Runtime Gas: 5,924,031 gas
Gas_and_Test_optimization Branch Runtime Gas: 5,896,048 gas

Sum Total Gas saved: 449,056 gas

USD saved on dai.sol(daily): $230 - $270
USD saved on dai.sol(monthly): $7_300 - $ 7_600
USD saved on dai.sol(yearly): $85_000 - $100_000
estimated at an average of 3_000-5_000 active users daily on the MakerDAO protocol-- (Check gas_report_dai.txt for full gas report)

(dai.sol)

• Implemented custom error messages.
• Upgraded the compiler from ^0.6.12 to ^0.8.0 which introduces new compiler friendly keywords like "now" and "type"
• The "now" keyword from older compiler versions becomes "block.timestamp"
• The once "uint256(-1)" which the EVM recognizes as the highest value of the uint256 bytes now becomes "type(uint256).max" in newwer compiler versions.
• Optimized the EVM compiler SLOAD from whenever function calls to storage variables directly and once.
• Remodeled the require statements for better error handling using if and revert statements.
• Implemented professional NatSpec comments.
• Implemented headers to every layout section.

(dai.t.sol)

• Implemented Vm Interface that introduces expectRevert and other testing utilities.
• Upgraded the compilar from ^0.6.12 to ^0.8.0 which introduces new compiler friendly keywords like "now" and "type"
• The "now" keyword from older compiler versions becomes "block.timestamp"
• The once "uint256(-1)" which the EVM recognizes as the highest value of the uint256 bytes now becomes type(uint256).max in newwer compiler versions.
• Implemented assertTrue() to ERC20 functions that returns bool
• Implemented professional NatSpec comments.

[DaiFoundation-DevOps]

All committers have signed the CLA.