fix(analytics, android, ios): cast item INDEX param to integer

[brojor]

Description

The React Native bridge converts all JS numbers to double, but the native Firebase SDK expects FirebaseAnalytics.Param.INDEX (which maps to item_list_index) as an integer/long. When a double is forwarded, Firebase does not recognise it as the standard ecommerce parameter — item_list_index ends up as (not set) in GA4 / BigQuery, breaking attribution of clicks/views to list positions.

The library already handles this exact problem for Param.QUANTITY in both native modules. This PR mirrors that conversion for Param.INDEX:

• Android (ReactNativeFirebaseAnalyticsModule.java): putLong(FirebaseAnalytics.Param.INDEX, (long) number)
• iOS (RNFBAnalyticsModule.m): item[kFIRParameterIndex] = @([item[kFIRParameterIndex] integerValue])

No JS / TS changes — the public API already accepts index: number, only the native coercion was missing.

Related issues

None filed upstream; happy to open one if preferred.

Release Summary

Fix item_list_index showing as (not set) in GA4 / BigQuery when index is provided on items[].

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • Yes
• My change supports the following platforms;
  • Android
  • iOS
  • Other (macOS, web)
• My change includes tests;
  • e2e tests added or updated in packages/**/e2e
  • jest tests added or updated in packages/**/__tests__
• I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

No tests added — the existing QUANTITY conversion (the precedent this PR follows) is also not covered by jest/e2e tests, since the coercion happens in the native modules below the JS bridge and there is no native test infra in the analytics package. Happy to add coverage if maintainers point me at the right place.

Test Plan

Verified in production via `patch-package` against `@react-native-firebase/analytics@22.3.0` in a live e-commerce app:

• Before: `item_list_index` arrives as `(not set)` in GA4 / BigQuery despite `index` being set on every item.
• After: `item_list_index` is populated with the correct integer position for `view_item_list`, `select_item`, and related ecommerce events.

🔥

---

Note

Low Risk
Small, localized change to native parameter coercion for analytics events; low risk aside from potential truncation if callers pass non-integer index values.

Overview
Ensures Firebase ecommerce items[] event params send INDEX/item_list_index as an integer type instead of a JS-bridge double.

On Android, ReactNativeFirebaseAnalyticsModule.toBundle now casts FirebaseAnalytics.Param.INDEX to long; on iOS, cleanJavascriptParams now coerces kFIRParameterIndex to an integerValue, mirroring existing QUANTITY handling.

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Code Review

This pull request adds support for the INDEX parameter in Firebase Analytics for both Android and iOS platforms. On Android, the parameter is converted from a double to a long, while on iOS, it is converted to an integer. A review comment suggests improving variable naming for better readability and notes a potential inconsistency in how numeric parameters are typed compared to the Firebase SDK expectations.