[Local Catalog] Implement POS catalog download & parsing for full sync

[jaclync]

For WOOMOB-1174

⚠️ Feel free to review only if the base PR #16041 doesn't require significant changes.

Description

This PR extends the POSCatalogSyncRemote implementation with basic catalog download functionality and returns the catalog of products and variations. Background download will be implemented separately in WOOMOB-1173.

Key Changes:

• Implemented downloadCatalog() method with mapping from a full list of POSProduct to products and variations based on whether the product type is variation or not (the API response schema could change later, I'm keeping this mapping logic in the networking layer for now)
• Created response model POSCatalog to contain arrays of products and variations
• Added test coverage for the downloadCatalog endpoint including success scenarios, error handling, and edge cases. The success case uses a mock response with a simple product, variable product, and 2 associated variations

Steps to reproduce

Just CI passing is sufficient, as the remote isn't used in the app yet.

Testing information

I tested with

let catalogResponse = try await syncRemote.generateCatalog(for: siteID)
print("Job ID: \(catalogResponse.jobID)")
let jobID = catalogResponse.jobID
var isNotComplete = true
while isNotComplete {
    let statusResponse = try await syncRemote.checkCatalogStatus(for: siteID, jobID: jobID)
    if statusResponse.status == .complete {
        isNotComplete = false
        print("Job complete, download URL: \(statusResponse.downloadURL)")
        if let downloadURL = statusResponse.downloadURL {
            let catalog = try await syncRemote.downloadCatalog(for: siteID, downloadURL: downloadURL)
            print("Downloaded \(catalog.products.count) products and \(catalog.variations.count) variations for siteID \(siteID)\nProducts: \(catalog.products)\nVariations: \(catalog.variations)")
        }
    } else {
        print("Job status: \(statusResponse.status), progress \(statusResponse.progress), waiting 2 seconds...")
        try await Task.sleep(nanoseconds: 2_000_000_000)
    }
}

in the app to verify that the products & variations counts are as expected for the site.

---

• 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 Prototype by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS Prototype
	Build Number	pr16042-287a8ec
	Version	23.1
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	287a8ec
	Installation URL	37esonqh1v2a8

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[joshheald]

Works well, thanks!

[joshheald]

We'll have to change the function signature when we do this. I don't think it will be an async returning function any more. The app will get a callback when it's done, and have to handle the data there instead of here.

[jaclync]

Yup, the background download could be tricky as we might need to handle related events from app delegate from this part of the documentation:

If your app is in the background, the system may suspend your app while the download is performed in another process. In this case, when the download finishes, the system resumes the app and calls the UIApplicationDelegate method application(_:handleEventsForBackgroundURLSession:completionHandler:). This method receives the session identifier you created in Creating a background URL session as its second parameter.

Going to start checking out the background download implementation today.