Add pull request template (Closes #430)

[CHASE3020]

Description

This pull request introduces a standardized `PULL_REQUEST_TEMPLATE.md` to guide contributors when submitting PRs. It prompts

contributors to describe their changes in detail, link to the relevant issue, select the type of change they're making, provide
testing notes, and confirm that their documentation has been updated. This template will automatically load when a new pull
request is opened, helping keep PR descriptions organized, consistent, and highly scannable for reviewers.

## Type of Change
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
- [x] Documentation update

## Testing Notes
- Verified that the `.github/PULL_REQUEST_TEMPLATE.md` file exists and is placed in the correct directory for GitHub to

automatically detect it.
- Confirmed the template includes all requested sections (Description, Linked Issue, Type of Change, Testing Notes, and
Checklist).

## Checklist
- [x] I have updated the documentation accordingly.
- [x] My changes generate no new warnings.
- [x] I have performed a self-review of my own code.

Closes #430

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