feat(remote_config): add Firebase Remote Config integration

[sharjeelyunus]

Firebase Remote Config Module

Summary

Adds an optional ensemble_remote_config module so apps can use Firebase Remote Config for A/B testing, feature flags, and runtime config in YAML. Off by default; enabled from the starter like other optional modules (Analytics, Stripe).

What's in this PR

• Ensemble core: Stub RemoteConfig / RemoteConfigStub and ensemble.remoteConfig in data context (property access, .get, .refresh, .setDefaults, .all(), .info()). No Firebase dependency in core.
• Module ensemble_remote_config: Implements Remote Config (fetch on startup, typed getValue, setDefaults, refresh, debug helpers, getAllValues, getInfo).
• Env-driven settings: remote_config_fetch_timeout and remote_config_minimum_fetch_interval environment variables control fetchTimeout and minimumFetchInterval (with safe defaults). Values are applied on init and re-applied before each fetchAndActivate() / ensemble.remoteConfig.refresh().
• Starter: useRemoteConfig flag, optional dependency and GetIt registration, enable script that also runs Firebase setup.
• Docs: README in the module (enable steps, usage, A/B testing guide, env-based settings, setDefaults behavior).

Usage

Method	Description	Example
Property access	Read a key; value is inferred as bool, num, or string.	ensemble.remoteConfig.my_key
get	Read with a custom default; type follows the default.	ensemble.remoteConfig.get('my_key', false)
getBool	Read as boolean with optional default.	ensemble.remoteConfig.getBool('flag', false)
getInt	Read as int with optional default.	ensemble.remoteConfig.getInt('max_items', 10)
getDouble	Read as double with optional default.	ensemble.remoteConfig.getDouble('ratio', 0.5)
getString	Read as string with optional default.	ensemble.remoteConfig.getString('cta_text', 'Try it now')
setDefaults	Register app-side defaults with Firebase; use at startup.	ensemble.remoteConfig.setDefaults({ flag: true, max_items: 10 })
all	Return a map of all keys to their current values (debug).	ensemble.remoteConfig.all()
info	Return metadata (initialized, lastFetchStatus, lastFetchTime, etc.).	ensemble.remoteConfig.info()
refresh	Manually re-fetch and activate Remote Config values (uses current env-based timeout/interval).	ensemble.remoteConfig.refresh()

How to enable

• Script: From starter/ run npm run hasRemoteConfig (or npm run enable and pick remote_config).
• Manual: Uncomment ensemble_remote_config in starter pubspec.yaml, set useRemoteConfig = true and uncomment the import and GetIt line in ensemble_modules.dart. Ensure Firebase is configured (google-services.json / GoogleService-Info.plist / web config).

Environment variables

remote_config_fetch_timeout: 10 # seconds, default 10
remote_config_minimum_fetch_interval: 3600 # seconds, default 3600 (1h)

• For local debugging you can temporarily set remote_config_minimum_fetch_interval: 0 to avoid throttling, then call ensemble.remoteConfig.refresh().
• In production, keep a higher interval to avoid unnecessary fetches.