Coupon Assets - audit

All of the Burnable tokens are sent to the contract `_owner` when deploying the contract. This could be a centralization risk as the anonymous deployer can distribute tokens without obtaining the consensus of the community. Any compromise to the deployer account that holds undistributed tokens may allow the attacker to steal and sell tokens on the market, resulting in severe damage to the project.

These functions invoke events without `emit` which is deprecated. ```solidity=290 RefundETH(owner, payee, amount); ``` ```solidity=303 RefundERC20(owner, payee, tokenContract, amount); ``` ```solidity=361 Transfer(address(0), owner, amount); ```

Functions that update state variables should emit relevant events as notifications.

During the code review, it was identified that the project is utilizing an outdated version of OpenZeppelin, specifically version 1.9 or earlier. The latest version of OpenZeppelin is 5.0, which introduces significant improvements in terms of security, functionality, and overall code quality. Using an outdated version of OpenZeppelin poses potential security risks and may result in vulnerabilities that have been addressed in the newer releases. It is crucial to stay up to date with the latest version to ensure the highest level of security for the project.