feat: create unit tests for beast skill

[fishonamos]

Pull Request Overview

📝 Summary

I added tests for the BeastSkill struct. The tests cover:

• Initialization of BeastSkill with valid skill spans
• Skill assignment for Light, Magic, and Shadow beast types
• Edge cases, such as empty skill spans
• Validation that only valid skill IDs are accepted
  This will ensure the BeastSkill struct behaves as expected.

Related Issues

• Closes 📝 [FEAT]: Add Unit Tests for BeastSkill Model #140

Type of Change

Mark with an x all the checkboxes that apply (like [x]).

• 📝 Documentation (updates to README, docs, or comments)
• 🐛 Bug fix (non-breaking change which fixes an issue)
• 👌 Enhancement (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)

🔄 Changes Made

What's Changed

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Implementation Details

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Technical Notes

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🔧 Tests Results

Describe the tests you performed to verify your changes.

Test Coverage

• Unit Tests
• Integration Tests
• Manual Testing

Evidence

Testing Notes

Include any special testing considerations or edge cases checked.

🔜 Next Steps

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[fishonamos]

Kindly review @coxmars