Refactor all tests to use named import syntax never import full files

[arthurgousset]

(House keeping)

Always use named import syntax, don’t import full files. This restricts what is being imported to just the named items, not everything in the file. Importing full files can result in solc complaining about duplicate definitions and slither erroring, especially as repos grow and have more dependencies with overlapping names.

Good: import {MyContract} from "src/MyContract.sol" to only import MyContract.
Bad: import "src/MyContract.sol" imports everything in MyContract.sol. (Importing forge-std/Test or Script can be an exception here, so you get the console library, etc).

Source: Foundry > Best Practices

For example:

This:

celo-monorepo/packages/protocol/test-sol/unit/common/FeeHandlerSeller.t.sol

Line 6 in e83b1b7

import { Test } from "celo-foundry/Test.sol";

Instead of this:

celo-monorepo/packages/protocol/test-sol/unit/common/Accounts.t.sol

Line 5 in e83b1b7

import "celo-foundry/Test.sol";

Not only is this better from a bug prevention perspective, but it also make it explicit where contracts are defined when they are inherited.