[Local catalog] Fix observation of variation attributes

[joshheald]

Follows #16399

Description

This PR updates the displayed variations in an item list when their names change.

Previously, we observed changes to the variation, but not its attributes. Attributes make up the name of a variation, so it meant we didn't update the name when we needed to.

To fix that, we observe the attributes and variation attributes, and make sure we delete and recreate them on incremental updates.

Test Steps

1. Open POS and perform a full sync in settings
2. Open a variable product
3. Edit the variable parent product's attributes in wp-admin
4. Pull to refresh to force an incremental sync
5. Observe that the variations names update
6. Edit the attributes of a few variations in wp-admin
7. Pull to refresh again
8. Observe that the names update

Screenshots

variation.name.changes.mp4

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

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 23.8. This milestone is due in less than 2 days. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

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[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	pr16400-1e785ef
	Version	23.7
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	1e785ef
	Installation URL	2tk40ac99e5fo

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[iamgabrielma]

LGTM!

[iamgabrielma]

Question: Does attributes need to be nullable here? (I think is always present but could be empty) Otherwise we can remove the optional and simplify the nil-coalescing below

[joshheald]

Good catch