Summary

This PR improves code quality in ivy_guc.c with the following changes:

• Fix typo in comment: "blow" → "below" (line 59)
• Remove trailing whitespace: Clean up comment formatting (line 187)
• Fix typo in gettext: "charater" → "character" (line 423)
• Fix error message: Remove double period (line 480)
• Add proper error codes: Include errcode() to ereport() calls for better PostgreSQL error handling:
  • ERRCODE_STRING_DATA_RIGHT_TRUNCATION for length validation errors
  • ERRCODE_INVALID_PARAMETER_VALUE for NLS parameter errors
• Performance optimization: Cache strlen() result in nls_case_conversion() function, changing complexity from O(N²) to O(N)
• Replace magic numbers: Use character constants ('a', 'z', 'A', 'Z') instead of ASCII codes for better readability

Test Plan

• Code compiles without warnings
• Regression tests pass
• Manual testing of NLS parameter validation
• Testing of case conversion functions