Support pull based approach for metadata fetching

This CL extends the OnDeviceIntelligenceService to support
fetching metadata for a given feature used via a pull-based approach.

*   Added new APIs in OnDeviceIntelligenceService and OnDeviceSandboxedInferenceService.
*   Refactored code to improve readability.

Context: go/odim-api-improvements

Flag: android.app.ondeviceintelligence.flags.on_device_intelligence_25q4
Bug: 372658837
Test: cts
Change-Id: I8444e202c553b749fef3f5b92b3ef9809e1eb523