[OpenSRP] Migrate Engine to KMP

[FikriMilano]

IMPORTANT: All PRs must be linked to an issue (except for extremely trivial and straightforward changes).

Fixes #2948

Description
Introduces engine-kmp, a new Kotlin Multiplatform module that ports the FHIR Engine to run on Android, iOS, and Desktop, JS/Wasm.

The migration replaces JVM-only dependencies (HAPI FHIR, Room Android, java.time, java.util.UUID, Timber, Gson) with multiplatform equivalents (kotlin-fhir, Room KMP, kotlinx-datetime, kotlin.uuid, Kermit, kotlinx-serialization).

What's done:

1. Create engine-kmp module

   • KMP module targeting Android, iOS x3, Desktop/JVM
   • Sample app proving Room KMP + Compose Multiplatform work together
   • Build config with platform-specific source sets

2. Core data model & interfaces

   • FhirEngine.kt — main interface with 12 suspend methods + search/count extensions
   • Database.kt — internal DB interface
   • LocalChange.kt, FhirEngineConfiguration.kt, DateProvider.kt, ContentTypes.kt
   • MoreResources.kt — resource type registry replacing JVM reflection (Class.forName() to KClass)
   • Logging.kt — Kermit-based logging facade replacing Timber

3. Indexing

   • 9 index entity data classes (StringIndex, DateIndex, DateTimeIndex, NumberIndex, QuantityIndex, TokenIndex, ReferenceIndex, UriIndex, PositionIndex)
   • ResourceIndices container with Builder pattern
   • ResourceIndexer — indexes FHIR resources using kotlin-fhir's FhirPathEngine.forR4()

Alternative(s) considered
Have you considered any alternatives? And if so, why have you chosen the approach in this PR?

Type
Migration

Screenshots (if applicable)

Checklist

• I have read and acknowledged the Code of conduct.
• I have read the Contributing page.
• I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA.
• I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
• I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project.
• I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally.
• I have built and run the demo app(s) to verify my change fixes the issue and/or does not break the demo app(s).

[ellykits]

@FikriMilano Can you recreate this via your own fork instead of OpenSRP's?

[FikriMilano]

moved to personal fork
#2952