Refactor rotate modifiers to a stricter no-op version for 0 degree rotations

Currently, rotate(0) (and normalized rotate(360)) may still apply driver-specific state changes (e.g. transparency/page metadata) even when pixels do not change.

For the next major release, refactor both GD and Imagick RotateModifier implementations so zero-angle rotation is a strict no-op (no pixel changes, no metadata side effects), and update tests to reflect the new contract.