Testing PR config

[RayStick]

Intended behaviour:

• The first person to add themselves as a reviewer on a PR is tagged as the main reviewer, and gets the main_rev_checklist.md in a comment.
• Any additional reviewers who add themselves get the rev_checklist.md in a comment.

[Copilot]

Pull Request Overview

This PR implements an automated reviewer checklist system that assigns different checklists based on reviewer order. The first person to add themselves as a reviewer gets the main reviewer checklist, while subsequent reviewers receive a supporting reviewer checklist.

• Changes workflow trigger from PR assignment to review requests
• Implements logic to differentiate between main and supporting reviewers based on count
• Standardizes placeholder replacement across both checklist templates

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
README.md	Adds documentation for the new main reviewer checklist feature
.github/workflows/rev_checklist.md	Creates supporting reviewer checklist template
.github/workflows/main_rev_checklist.md	Standardizes placeholder name from __MAINREV__ to __REV__
.github/workflows/main-reviewer.yml	Refactors workflow to handle both main and supporting reviewer checklists

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