feat: integrate eppo module with android-sdk-framework (v3 → v4 migration)

[typotter]

Summary

Migrates the eppo module from v3 SDK to v4 framework, completing the integration started in #248.

Dependencies

Depends on: #248 (must be merged first)

Major Changes

EppoClient Migration (v3 → v4)

• Extends AndroidBaseClient from framework instead of v3 BaseEppoClient
• Removes v3 dependencies:
• Adds framework dependency: module
• Removes old storage classes: ConfigurationStore, ConfigCacheFile, BaseCacheFile (now in framework)

New v4 Components

• OkHttpEppoClient: HTTP client implementation with Android logging
• JacksonConfigurationParser: JSON parsing for v4 FlagConfigResponse format
• Jackson adapters: Custom serializers/deserializers for EppoValue, FlagConfigResponse, dates

Test Infrastructure Fixes (Critical for 46/46 tests passing)

1. TestConfigCacheFile.cacheFileName(): Fixed to match framework format
   • Was: eppo-sdk-flags-cloud.eppo.api.Configuration-{suffix}.bin
   • Now: eppo-sdk-flags-{suffix}.ser
2. waitForPopulatedCache(): Removed redundant .ser suffix
3. Unclosed OutputStreams: Added try-with-resources (3 locations)
4. testDifferentCacheFilesPerKey: Simplified to copy actual cache instead of custom JSON

Example App Enhancements

• CustomClientActivity: Demonstrates custom HTTP client injection
• GsonConfigurationParser: Example alternative to Jackson parser
• HeaderInjectingEppoClient: Example custom HTTP headers

Test Results

• ✅ 46/46 instrumentation tests passing locally
• ✅ Framework module builds independently
• ✅ Eppo module builds with v4 dependencies
• ✅ No breaking API changes for SDK users

Migration Notes

• Cache files use .ser extension (Java serialization)
• Configuration format changed from v3 to v4 JSON structure
• All existing tests adapted and passing