Added uncovered files detection - Issue #529

[Victowolf]

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Summary

This PR enhances package:coverage by adding support for detecting uncovered files.

Changes

• Implemented logic to identify files that are missing from coverage reports.
• Updated test cases to validate detection of all files.
• Ensured compatibility with existing workflows.

Testing

• Ran dart test and all tests passed successfully.

Issue Reference

• Resolves Add a tool to find uncovered files #529.