feat: support single-letter name extraction from alphanumeric patterns

[meabed]

Summary

• Enhanced name detection to properly handle patterns like j7.d2
• Now correctly extracts single letters as valid names when they appear with numbers
• Improves parsing of email addresses with single-letter initials combined with numbers

Changes

• Modified parseCompositeNamePart function to accept single letters after number removal
• Added allowSingleLetter parameter to isLikelyName function for explicit single-letter validation
• Updated validation logic to allow single letters in appropriate contexts
• Added test cases for j7.d2 pattern verification

Test Results

All tests pass successfully. The implementation now correctly:

• Extracts 'J' and 'D' from j7.d2@example.com
• Extracts 'A' and 'B' from a1.b2@example.com
• Still extracts 'John' and 'Due' from john1.due2@example.com
• Maintains backward compatibility for all other patterns

Example

detectName('j7.d2@example.com')
// Returns: { firstName: 'J', lastName: 'D', confidence: 0.85 }

Fixes the handling of single-letter alphanumeric patterns as requested.