Restructure pipeline to include patch verification

[coloursofnoise]

Restructures build pipeline to verify patches against Celeste earlier, (hopefully) failing if the patch fails.

• PR builds should not have access to vanilla files, patch verify and lib-stripped steps are skipped
• Main build artifact should always be uploaded even on failure, and Olympus artifact should still be uploaded for builds that don't access vanilla files

Also adds caching for Vanilla files with key including pipeline secrets for security