Improve registryAuth logic

[PE39806]

• Fix incorrect "read-only" access logic in isReadOnlyActions
• Replace generateAccess(scope: any): Access with parseResourceScope(input: string): Access[] to enforce correct Resource Scope Grammar
• Add NodeCache to reduce reading files from disk
• Refactor out constants
• Rename getAccessToken & getRefreshToken to issueAccessToken & issueRefreshToken for clearer intent
• Harden scope parsing with explicit validation and clearer error handling
• Improve error handling and logging around JWT signing and auth failures
• Improve and extend tests

[GB907762]

This all looks functionally correct. There's a couple of things, but they may just be really picky.