Add DynClone to make the builder cloneable

[stevefan1999-personal]

This PR uses https://github.com/dtolnay/dyn-clone and modified some traits to use DynClone, so that eventually the Builder can now be Clone. Notice while the cargo test fully passes for this, this is a potentially ABI breaking change.

[notriddle]

This change makes sense to me, but will definitely require a major version bump.

cc @lnicola