feat: support validate in args definition

[peterroe]

🔗 Linked issue

Fix: #84

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 39 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@7ee947b). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/args.ts	0.00%	17 Missing ⚠️
src/types.ts	0.00%	9 Missing ⚠️
playground/commands/deploy.ts	0.00%	8 Missing ⚠️
src/command.ts	0.00%	5 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##             main     #87   +/-   ##
======================================
  Coverage        ?   0.00%           
======================================
  Files           ?      13           
  Lines           ?     950           
  Branches        ?      13           
======================================
  Hits            ?       0           
  Misses          ?     937           
  Partials        ?      13           

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[janniks]

Should validate always fail and show the failure string if it's a string (even if not an required arg)?

[janniks]

Looks good to me, had one comment. 👏