chore: refactor v5-specific code out of core packages

[kzantow]

This PR refactors some code to eliminate dependencies on v5 in core packages, including renaming grypeDB import aliases to v5 for increased clarity.

After this PR, the only references to v5 specific code, outside of the db/v5 packages are:

• loading the vulnerability db (which is necessary in some way until switching to v6)
• differ (which I believe is not going to be ported to v6 and should probably get moved under the db/v5 package)
• tests mocking vulnerabilities using v5 data structures

This PR does not adjust any of the tests or the vulnerability.Provider/MetadataProvider interfaces

This is a prerequisite for #2132