Fix prices missing when products are restored from cache

[ianrumac]

Changes in this pull request

Cached config writes product reference names as product, but the decoder only read reference_name. Restoring config therefore turned names such as offer into empty strings, leaving prices unavailable to named paywall bindings. Accept both fields, preferring the API's reference_name, so existing caches restore correctly without changing the WebView payload.

Adds serialization, request-cache/template, and Android WebView regression tests, plus an Unreleased changelog entry.

Validation

• Focused JVM tests pass, including config round-trip, same-build refresh, and the full-cache-reset control.
• Both WebView tests pass on a Pixel 8 emulator running Android 14.
• Before the fix, three JVM reproduction tests and the cached-config WebView test failed; the latter rendered an empty string instead of €23.99.
• Emulator coverage uses a minimal price-binding page and fixture prices, not the customer's hosted paywall or RevenueCat integration.
• New test files pass ktlint. Existing formatting violations remain elsewhere in ProductItem.kt.

Checklist

• All unit tests pass (focused tests run; full suite not run).
• All UI tests pass (two focused emulator tests run).
• Demo project builds and runs (not run).
• I added/updated tests.
• I added an entry to CHANGELOG.md.
• I have run ktlint in the main directory and fixed all issues (new tests pass; pre-existing source issues remain).
• Documentation considered: no public API changes.
• I have reviewed the contributing guide.