Add Initial Test Suite (Synonym Reuse & Duplication Detection)

Currently, Smart Icons Kit has no automated tests. To improve reliability and make future contributions safer, we need to set up a testing framework and add the first set of tests.

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Tasks

• ⚙️ Set up a testing framework (Jest recommended).
• 🧪 Add a test to check if a synonym is already used by another icon.
• 🧪 Add a test to detect duplicate icon definitions.

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Why This Matters

Tests are essential to ensure the library behaves as expected. Adding even basic coverage will help catch regressions early and make it easier for new contributors to contribute confidently.

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🏷️ Hacktoberfest Note

This is a good first issue for Hacktoberfest contributors 🎉

If you’re new to open source, this issue will help you get started by:

• Learning how to set up a test framework in a JS/TS project.
• Writing meaningful tests for a real-world package.
• Contributing to an actively maintained open-source project.