Remove unused Factorial method and related code

[konard]

Summary

This PR removes the unused Factorial method and related code as requested in issue #59. After analysis, I confirmed that:

• The Factorial method is no longer used anywhere in the LinksPlatform ecosystem
• The Catalan method now uses precalculated values and doesn't depend on Factorial calculations
• Only usage was in performance benchmarks within the Numbers repository itself

Changes Made

• ✅ Removed the Factorial<TLinkAddress> method from Math.cs
• ✅ Removed the _factorials array (no longer needed)
• ✅ Removed the MaximumFactorialNumber constant
• ✅ Removed the CurrentFactorialImplementation benchmark test
• ✅ Maintained all existing functionality for Catalan and IsPowerOfTwo methods
• ✅ All tests pass after removal

Test Plan

• Build succeeds with no errors
• All existing tests continue to pass
• Catalan method works correctly with precalculated values
• IsPowerOfTwo method remains unaffected
• Benchmarks can still run (other factorial alternative implementations remain for comparison)

Verification

The removal was verified by:

1. Searching the entire LinksPlatform ecosystem - no external usage found
2. Confirming Catalan method uses _catalans array, not factorial calculations
3. Running full test suite to ensure no regressions
4. Building successfully after removal

Fixes #59

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