feat(kotlin-platform-sdk): add diagnostics module (Phase 2.3)
New diagnostics package in kotlin-platform-sdk:
- DiagnosticsTypes: Session, TraceSpan, LogEntry, Breadcrumb, NetworkRequest
- DiagnosticsClient: singleton with StateFlow for reactive state
- BreadcrumbTrail: ring buffer (max 100) for timeline
- NetworkInterceptor: OkHttp interceptor for HTTP capture
- DeviceStateCollector: battery, memory, storage, network
- 16+ JUnit tests for types and breadcrumbs
Features:
- configure()/start()/stop() lifecycle
- trace() suspend span wrapper
- log() with breadcrumb integration
- ETag-based config polling
- 30-second batch flush
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