Make PR template form clearer and more concise

[Sevans711]

Closes #1696

Overview

Makes the PR template form more concise.

Minor expansions of this PR's scope:

• Clarified language in a few places throughout the form and rearranged comments slightly. I think these changes will make the form clearer and easier to read quickly.
• Removed the suggestions to delete entire sections of the checklist. There are far fewer items now (roughly half as many) so I think it shouldn't be too hard to just mark items as [N/A]…? This also helps reduce mental load; instead of "consider if the whole section applies, then consider if each point applies" it becomes simply "consider if each point applies".

I hope these changes would all improve contributor experience. But, they are all based on my subjective opinions and intuitions. Please let me know if you have any questions or concerns, or would prefer different phrasing!

PR Checklist

General

• An issue is created and linked
• Added appropriate labels (if your uxarray repo permissions allow it)
• Filled out Overview and Expected Usage (if applicable) sections

AI Disclosure

AI Usage: GitHub Copilot suggestions show up inline in my editor and maybe influenced my thought processes here, but I don't remember if I actually accepted any of them directly.

• I take responsibility for all AI-generated content in my PR.
• I have tested all AI-generated content in my PR.