Dynamic dashboard: Fix thread priority inversion warning

[itsmeichigo]

Closes: #12536

Description

When syncing stats on the dashboard screen, we track the performance after the syncing completes. These were called immediately inside the reloadData methods on StorePerformanceViewModel and TopPerformersDashboardViewModel. Both methods are async and marked with @MainActor for the results to be returned on the main thread.

When sending Tracks events, the events are created and saved to CoreData using performAndWait. If I understand correctly, this is to make it safe to send events continuously and synchronously. However, this happens on a background thread and blocks the async methods running on the main thread, causing potential UI hang, thus Xcode logs a warning for thread priority inversion.

To fix this issue, I created a separate publisher to keep track when syncing stats completes, and observe the data stream in a background thread before sending Tracks events. This makes sure that Tracks doesn't block the async method on the main thread.

Testing instructions

• Build and run the app.
• Log in to a store and enable both Performance and Top Performers cards.
• Leave the app idle for 3-5 minutes. Confirm that there is no warning in Xcode log about priority inversions by Thread Performance Checker.

Screenshots

N/A

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• [x] I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS
	Build Number	pr12629-470e292
	Version	18.4
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	470e292c921d0290c1fea60e5a251f2f999ddb30
	App Center Build	WooCommerce - Prototype Builds #8922

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