fix: keep transitive scanning with --offline-vulnerabilities

[gotgolem]

Overview

Fixes #2775.

--offline-vulnerabilities is documented as only switching vulnerability matching to the local DB, but it was also causing Scalibr to filter out network-backed plugins.
That meant transitive dependency scanning was disabled even when --no-resolve was not passed.

This PR keeps that behavior scoped to the full --offline flag instead.

Details

I added a separate ScannerActions.PluginNetworkDisabled field and wire it from --offline.

CompareOffline still controls the local vulnerability DB path. The source and container scan paths now use PluginNetworkDisabled when setting Scalibr's network capability.

License behavior under --offline-vulnerabilities is intentionally left unchanged in this PR.

Testing

• go test ./pkg/osvscanner ./cmd/osv-scanner/internal/helper
• go test ./cmd/osv-scanner/scan/source -run TestCommand_Transitive -count=1

Also ran:

• ./scripts/run_tests.sh
  • Fails locally on unrelated snapshot drift from external data changes.

Checklist

• I have signed the Contributor License Agreement.
• I have run the linter using ./scripts/run_lints.sh.
• I have run the unit tests using ./scripts/run_tests.sh.
• I have made my commits and PR title follow the Conventional Commits specification.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.29%. Comparing base (bc422e5) to head (c6d3c01).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2783      +/-   ##
==========================================
+ Coverage   79.26%   79.29%   +0.02%     
==========================================
  Files         122      122              
  Lines        8258     8259       +1     
==========================================
+ Hits         6546     6549       +3     
+ Misses       1329     1328       -1     
+ Partials      383      382       -1     

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[another-rex]

LGTM, thanks!

[another-rex]

Not too sure if this test is that useful, since it's just testing 1 if statement essentially.

[gotgolem]

Thanks, fair point.

I added it as a regression guard for the CompareOffline / PluginNetworkDisabled split, but the transitive scan test covers the user-visible behavior. I can drop this one if you prefer :)

[another-rex]

Hmm... Let's keep it for now since it runs pretty fast, if we find it causing friction later we can remove it.

[gotgolem]

Sounds good, thanks for the review!