[Woo POS] Extract order creation to aggregate model

[joshheald]

Closes: #14417

Description

Sorry this is so big... I really couldn't find a way to reduce the size without also breaking the app in the process...

This PR moves order creation/syncing, and the associated OrderState, to the new aggregate model.

I've also avoided exposing the order; all we need to actually show from it is the totals, so those are included in the order state now.

Tests mostly work, but there are some which aren't practical in the TotalsViewModelTests at the moment. Inline notes in the comments, and as I move more state into the aggregate model I'll be able to reinstate them (as tests on the aggregate model)

Testing information

This requires smoke testing of the order creation process, and some of the payments actions.

• Tapping checkout after adding items to the cart should show the correct totals
• Going back to edit the cart, then checking out again, should also show the correct totals
• If you have a card reader connected, it should be prepared for payment after the order syncs
• If you don't have a card reader connected, connecting one once you're on the checkout screen should automatically prepare it for payment.
• If you disconnect your reader on the checkout screen, after the order has synced, then reconnect it, it should be prepared for payment.
• If there's an API error while making the payment intent, the Edit order button should take you back to the item list (breakpoint on https://api.stripe.com/v1/payment_intents). Note that there's an issue even in trunk with the try again option on this error: the Stripe SDK doesn't always make the expected request, but instead says that the user is offline sometimes.
• If there's an API error while submitting the payment intent to WCPay, it should check the order to see whether payment was successful (breakpoint on response of https://public-api.wordpress.com/rest/v1.1/jetpack-blogs/*/rest-api/ after you tap the card)
• If we can't get the order details in the above situation, it should show an error with the Try again and New order actions (additional breakpoint on https://public-api.wordpress.com/rest/v1.1/jetpack-blogs/*/rest-api/?json=true&path=/wc/v3/orders/*)

Screenshots

https://github.com/user-attachments/assets/1c1550b5-e0b4-4db9-ad1a-60d927d93d51

---

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

Reviewer (or Author, in the case of optional code reviews):

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

• [x] The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• [x] Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• [ ] Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on all devices (phone/tablet) and no regressions are added.

[dangermattic]

	1 Warning
:warning:	This PR is larger than 300 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.

Generated by :no_entry_sign: Danger

[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	pr14437-333e8b1
	Version	21.1
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	333e8b1170ad36e67944a5a6f1cc41efaa939ca2
	App Center Build	WooCommerce - Prototype Builds #11631

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[iamgabrielma]

👋 I started the code review but haven't had time to test any flow, if nobody beats me to it I can continue tomorrow.