Update PR template and improve example validator script

[222448082Ashen]

Revamps the pull request template for clarity and geometry example validation instructions. Adds single-example validation mode to usage-examples-testing-script.cjs, enabling reliable checks for flat-file usage example layouts.

Description

Please include a summary of the changes and the related issue. Please also include relevant
motivation and context. List any dependencies that are required for this change.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as
  expected)
• Documentation (update or new)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can
reproduce. Please also list any relevant details for your test configuration.

Testing Checklist

• Tested in latest Chrome
• Tested in latest Firefox
• npm run build
• npm run preview

Checklist

Please delete options that are not relevant.

If involving code

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

If modified config files

• I have checked the following files for changes:
  • package.json
  • astro.config.mjs
  • netlify.toml
  • docker-compose.yml
  • custom.css

Folders and Files Added/Modified

Please list the folders and files added/modified with this pull request and delete options that are not relevant.

• Added:
  • folder/folder
  • folder/folder
• Modified:
  • folder/file
  • folder/file

Additional Notes

Please add any additional information that might be useful for the reviewers.

[netlify]

❌ Deploy Preview for splashkit failed.

Name	Link
🔨 Latest commit	90fa463
🔍 Latest deploy log	https://app.netlify.com/projects/splashkit/deploys/6947c617b2ddc50008b57f7e