Add test coverage for findClosestRationalAngle

[Copilot]

The findClosestRationalAngle function had no test coverage.

Changes

• src/lib_test.ts: 27 tests covering exact matches, approximate angle finding, normalization (>360°, negative), and edge cases
• deno.json: Added test task
• TEST_README.md: Test documentation

Test Coverage

// Exact matches
findClosestRationalAngle(45)    // → 45°
findClosestRationalAngle(-45)   // → -45°

// Approximation
findClosestRationalAngle(44)    // → 45°
findClosestRationalAngle(30)    // → 26.565° (arctan 1/2)

// Normalization
findClosestRationalAngle(405)   // → 45° (405 % 360 = 45)
findClosestRationalAngle(-30)   // → -26.565° (normalizes to 330°)

Run with: deno task test

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Original prompt

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This section details on the original issue you should resolve

<issue_title>Add tests for findClosestRationalAngle function</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add tests for findClosestRationalAngle function #6

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