Fix: Use visibility.base consistently in generateHelpNames for .longWithSingleDash

[AkshatRaj00]

Summary

This PR fixes an inconsistency in generateHelpNames(visibility:) in HelpGenerator.swift where the .longWithSingleDash case used the full visibility description instead of visibility.base, while the .long case correctly used visibility.base.

Fixes #901

The Bug

// BEFORE (inconsistent)
case .long(let helpName):
  return .long("\(helpName)-\(visibility.base)")           // ✅ uses .base
case .longWithSingleDash(let helpName):
  return .longWithSingleDash("\(helpName)-\(visibility)")  // ❌ uses full visibility

The Fix

// AFTER (consistent)
case .long(let helpName):
  return .long("\(helpName)-\(visibility.base)")
case .longWithSingleDash(let helpName):
  return .longWithSingleDash("\(helpName)-\(visibility.base)")  // ✅ now matches .long

Impact

• One-line change with no API breakage
• Affects only commands that configure helpNames with .longWithSingleDash at non-default (hidden/private) visibility levels
• Ensures -help-hidden and --help-hidden use the same suffix generation logic

Testing

Existing tests for help generation should continue to pass. The affected code path is only triggered when:

1. helpNames includes .longWithSingleDash
2. visibility.base != .default (i.e., .hidden or .private)

No new tests are broken by this change.