fix(detector/vuls2): fix post convert bugs

[shino]

What did you implement:

• Please review/merge chore(detector/vuls2): check downloaded time before updating db #2077 first 🙏

• Fix data source preference bug.

  • Prior to this, oval v1 is prefered to v2

• Fix root id selection bug.

  • Prior to this, selection of 3+ root IDs are buggy (range map dependent)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Using vuls-compare.

ref: #2075 (comment)

Checklist:

You don't have to satisfy all of the following.

• Write tests
• Write documentation
• Check that there aren't other open pull requests for the same issue/feature
• Format your source code by make fmt
• Pass the test by make test
• Provide verification config / commands
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES

Reference