refactor: update test coverage command and add new tests for collection quality and storage behavior

- Changed the test coverage command in package.json to use 'c8' for improved coverage reporting.
- Added a test to verify that confidence reports medium collection quality for partial collection.
- Introduced a test to ensure localStorage adapter is disabled when storage is unavailable.
- Added a test to check that storage state tolerates legacy entries without seenCount.

Author: MADEVAL