Read `zero_decimal_place_countries` from workflow screens (#4061)

Workflow paywalls showed decimal prices in TWN/KAZ/MEX/PHL/THA/IND.
`WorkflowScreen` never decoded `zero_decimal_place_countries`, so it
defaulted to empty. Backend side is RevenueCat/khepri#24207.

https://github.com/RevenueCat/purchases-ios/pull/7474

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Small deserialization/mapping fix using an existing serializer; no
auth or purchase-flow changes.
> 
> **Overview**
> Workflow paywalls now pick up `zero_decimal_place_countries` from the
backend instead of always treating it as empty, so prices in those
countries can render without decimals.
> 
> `WorkflowScreen` deserializes the store-keyed JSON via
`GoogleListSerializer` (Google list only) and `WorkflowScreenMapper`
forwards it into `PaywallComponentsData`. Defaults to empty when the
field is missing.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
52dbf1972f39b4e6bf0e8d86fca4aa1a538b18b5. Bugbot is set up for automated
code reviews on this repo. Configure
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<!-- /CURSOR_SUMMARY -->

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Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>