Stats: Refactor "stats-redirect" folder

[dognose24]

This is a follow-up of https://github.com/Automattic/wp-calypso/pull/95436.

Proposed Changes

• Remove the unnecessary StatsRedirectFlow component.
• Rename the stats-redirect folder to stats-page-loader.
• Wrap Stats purchase page with StatsPageLoader to utilize purchase data.

Why are these changes being made?

• Remove the unnecessary redirecting component and rename the folder to correspond to its behavior.

Testing Instructions

• Spin this change up with the Calypso Live branch.
• Navigate to the Stats pages and ensure everything is not changed.
• Navigate to the Stats purchase page: /stats/purchase/{site-slug}?productType=commercial.
• Ensure the purchasable tiers are based on the current tier.

Pre-merge Checklist

• [ ] Has the general commit checklist been followed? (PCYsg-hS-p2)
• [ ] Have you written new tests for your changes?
• [ ] Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• [ ] Have you checked for TypeScript, React or other console errors?
• [ ] Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• [ ] Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• [ ] For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?