[WOOMOB-359] Fix customer mapper copying billing address into shipping fields

[kidinov]

Description

Partially addresses WOOMOB-359

WCCustomerMapper.mapToModel() was mapping dto.billing fields into all shipping address fields instead of dto.shipping. The reverse mapping in mapToDTO() had the same bug — it wrote model.billing* fields into the Shipping DTO.

This meant that when a registered customer was selected during order creation, the app fetched their full data from /wc/v3/customers/{id} (which returns separate billing and shipping objects), but then threw away the shipping data and duplicated billing into both addresses.

What this fixes: Registered customers (those with a WordPress user account, user_id > 0) now correctly get their shipping address populated from the API response.

What this does NOT fix: Guest customers found via the analytics API (wc-analytics/reports/customers) still show billing data in both address fields. This is because the analytics API returns only a single flat set of address fields — there is no shipping address in the response. Fixing that requires either backend changes or switching to a different API endpoint (see the peaMlT-16R-p2 for details).

The existing tests used identical values for billing and shipping, so they never caught this bug. Updated them to use distinct values.

Test Steps

1. On a WooCommerce site, ensure you have a registered customer with different billing and shipping addresses
2. Start a new order creation
3. Tap "Add customer details"
4. Select the registered customer (the one with a username shown)
5. Verify that Shipping Address shows the actual shipping data
6. Verify that Billing Address shows the actual billing data
7. Confirm the two addresses are different

Images/gif

• I have considered if this change warrants release notes and have added them to RELEASE-NOTES.txt if necessary. Use the "[Internal]" label for non-user-facing changes.

[wpmobilebot]

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

	App Name	WooCommerce Android
	Platform	📱 Mobile
	Flavor	Jalapeno
	Build Type	Debug
	Build Number	736
	Version	24.4-rc-1
	Application ID	com.woocommerce.android.prealpha
	Commit	7507085
	Installation URL	67ikd83g05cdg

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

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 39.61%. Comparing base (4594cda) to head (7507085).
⚠️ Report is 3 commits behind head on trunk.

Files with missing lines	Patch %	Lines
...s/android/fluxc/model/customer/WCCustomerMapper.kt	50.00%	0 Missing and 9 partials ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##              trunk   #15575   +/-   ##
=========================================
  Coverage     39.61%   39.61%           
  Complexity    11330    11330           
=========================================
  Files          2260     2260           
  Lines        130516   130516           
  Branches      18298    18298           
=========================================
  Hits          51700    51700           
  Misses        73522    73522           
  Partials       5294     5294           

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