optimize and make sure unused-imports is accurate

It was added in https://github.com/crytic/slither/pull/2392 but it is really slow and has some edge cases e.g.
this is wrong
```
The following unused import(s) in src/universal/CrossDomainMessenger.sol should be removed:
-import { Initializable } from "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol"; (src/universal/CrossDomainMessenger.sol#4)
```
`slither contracts.zip --detect unused-import `
[contracts.zip](https://github.com/user-attachments/files/15597731/contracts.zip)