[Shipping labels] Add networking layer support for label status endpoint

[rachelmcr]

Part of: #14053

Description

This adds the Networking layer support for checking the status of a label after purchasing it. It can be used immediately after the purchase request to poll for the completed purchase.

How

• The response can be decoded as the existing ShippingLabelStatusPollingResponse, so we keep using that model.
• Introduces a new mapper because the new endpoint only returns a single label's status at a time.
• Introduces the new endpoint in WooShippingRemote.
• Adds a mock response and unit test support.

Testing information

This endpoint is not yet used in the app; confirm unit tests pass.

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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.

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:

• 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.
• 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.

[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	pr14488-9c0c256
	Version	21.1
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	9c0c256
	App Center Build	WooCommerce - Prototype Builds #11760

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

[rachelmcr]

These changes are complete but I'm waiting for checks to pass. Feel free to merge this, or I will merge it when I'm back from AFK.