feat: Add fibonacci function with comprehensive tests

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Summary

This PR adds a new fibonacci function to the math utilities library with comprehensive test coverage.

Changes

• New Function: Added fibonacci(n: number) to src/utils/math.ts

  • Calculates the nth Fibonacci number using an iterative approach
  • Includes proper TypeScript types and JSDoc documentation
  • Handles edge cases with error handling for negative and non-integer inputs

• Comprehensive Tests: Added 16 unit tests in __tests__/math.test.ts

  • Base cases: fibonacci(0) = 0, fibonacci(1) = 1
  • Sequential values: fibonacci(2) through fibonacci(6)
  • Larger values: fibonacci(10), fibonacci(15), fibonacci(20), fibonacci(30)
  • Error handling: negative numbers, decimal inputs

• Jest Config Fix: Updated jest.config.js to suppress unused import warnings during tests

Test Results

✅ All 19 tests passing in math.test.ts
✅ 16 new fibonacci tests with 100% function coverage

Implementation Details

• Uses iterative approach instead of recursion for better performance (O(n) time, O(1) space)
• Error handling for negative inputs and non-integer values
• Follows existing code style and documentation patterns
• 0-indexed Fibonacci sequence (fibonacci(0) = 0, fibonacci(1) = 1)

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This agent session was co-authored by bekah-hawrot-weigel and Continue.