feat: expose devcycleClient property from DevCycleProvider

[jonathannorris]

Expose DevCycleClient from DevCycleProvider

Addresses the need to access proprietary DevCycle features while using the OpenFeature API, as outlined in #262.

Based on the work from PR #263 by @nnoel-grubhub

Changes:

• ✨ New public property: devcycleClient provides access to the underlying DevCycleClient instance
• 📝 Consistent naming: Updated to camelCase convention (devcycleClient, _devcycleClient)
• 🧪 Enhanced testing: Added comprehensive tests for property access and error cases

Usage:

val provider = DevCycleProvider(sdkKey, context)
OpenFeatureAPI.setProviderAndWait(provider)

// Access proprietary features like allFeatures() for analytics
val allFeatures = provider.devcycleClient.allFeatures()

Closes #262

[Copilot]

Pull Request Overview

This PR exposes the underlying DevCycleClient instance through a public property on DevCycleProvider, allowing access to proprietary DevCycle features while using the OpenFeature API.

• Added public devcycleClient property with error handling for uninitialized state
• Renamed internal field from devCycleClient to _devcycleClient for consistency
• Enhanced test coverage for property access and error scenarios

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
DevCycleProvider.kt	Added public devcycleClient property and renamed private field to _devcycleClient
DevCycleProviderTest.kt	Added tests for property access when client is initialized and uninitialized