fix: simplified imports and rm unused variable

[wei3erHase]

This PR aims to make the GetTradeableOrder library easily inherited by other repos. Also it removes the unused tradedAmountToken0 from the library.

Pending issues addressed in [draft] #98:

• [ ] installed OpenZeppelin is 4.9.0, Math Rounding enum are different than 5.0.2 (latest)
• [ ] OZ 5.0.2 deprecated safeApprove (which brings tests errors on the "when approve returns false" expectations)