Tests: Remaining budget proposal validation

[kneerose]

List of changes

• Added remaining budget proposal validation:
  1. Proposal ownership
  2. Problem statements and proposal benefits
  3. Proposal details
  4. Administration and Auditing
  5. Submit
• Refactored the validation tests

Checklist

• related issue
• My changes generate no new warnings
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the changelog
• I have added tests that prove my fix is effective or that my feature works

[github-actions]

✅ All checks succeeded

[github-actions]

✅ All checks succeeded

[github-actions]

✅ All checks succeeded

[github-actions]

✅ All checks succeeded

[github-actions]

✅ All checks succeeded

[github-actions]

✅ All checks succeeded