fix: make the deny check respect pkg namespaces

[dominikvagner]

Summary

This adds a namespace condition into the deny check. This will fix an issue where the check would deny different packages than those actually provided.
Also adds a test for this and fixes one test present by providing package URLs.

Testing steps

Steps to reproduce the behavior:

1. Go to any project with some packages.
   (ex.: a repo that has the valid eslint pkg as a dependency)
2. Have a config with a denied package, that has the same name, but a different namespace.
   (ex.: deny the malware @typescript_eslinter/eslint pkg)
3. Run the action.
4. Verify that it doesn't list the regular eslint as a denied package.

Closes: #1014

[Copilot]

Pull Request Overview

This PR enhances the package denial logic to include namespace checking, preventing false positives when packages share the same name but belong to different namespaces. The getNamespace call is refactored to be computed once per change and reused across both denied packages and denied groups checks.

Key changes:

• Added namespace comparison to the denied packages matching logic
• Moved namespace extraction outside the loops for better code reuse and performance
• Added test coverage for namespace differentiation scenarios

Reviewed Changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated no comments.

File	Description
src/deny.ts	Refactored to extract namespace once per change and added namespace check to denied packages logic
dist/index.js	Compiled JavaScript output reflecting the source changes
tests/deny.test.ts	Added test for namespace differentiation and updated existing test data with explicit package URLs

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