Turn {magick} into a Suggests dependency instead of a Imports?

[trevorld]

• Five-ish patterns depend on {magick} (technically gradient only needs it if not using R 4.1 gradient features)
• Some users who don't use those patterns have expressed pain in installing {magick} since you need to also install C++ header files to install on Linux
• If we do so we would need to check if namespace exists and throw informational error message that they need to install {magick} to use those patterns.