Add placement and targeting context to paywall events

[dpannasch]

Include presentedOfferingContext (placementIdentifier, targetingRevision, targetingRuleId) in paywall event serialization so that events & charts can utilize those dimensions.

Checklist

• If applicable, unit tests
• If applicable, create follow-up issues for purchases-ios and hybrids

Motivation

Description

---

Note

Medium Risk
Adds a new optional presented_offering_context payload to paywall events; while backwards-compatible in the client, it changes analytics/telemetry schema and could impact backend ingestion or downstream parsing if not handled.

Overview
Paywall event payloads now optionally include placement and targeting metadata via a new presented_offering_context object (placement identifier, targeting revision, targeting rule id).

Both PaywallStoredEvent.toBackendEvent() and PaywallEvent.toBackendStoredEvent() populate this field only when placement/targeting data exists (otherwise it remains null), and tests are expanded to validate request bodies, round-trip serialization, and backwards-compatible deserialization of older stored events without the new field.

^{Written by Cursor Bugbot for commit 9b96692. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

❌ Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.41%. Comparing base (b6b6349) to head (9b96692).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
...revenuecat/purchases/common/events/BackendEvent.kt	90.90%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3253      +/-   ##
==========================================
+ Coverage   79.38%   79.41%   +0.02%     
==========================================
  Files         357      357              
  Lines       14347    14362      +15     
  Branches     1959     1963       +4     
==========================================
+ Hits        11389    11405      +16     
+ Misses       2154     2152       -2     
- Partials      804      805       +1     

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[tonidero]

Looking great! If we've tested this and the backend is already accepting the new propert, let's 🚢