[FSSDK-11589] Add go-sdk logic to support agent for cmab

[Mat001]

Added CMAB (Contextual Multi-Armed Bandit) support to go-sdk for Agent integration:

1. CMAB Service: Core service that makes HTTP calls to external CMAB prediction endpoints
2. CMAB Cache: LRU cache with TTL to store prediction responses and reduce API calls
3. CMAB Configuration: Settings for request timeouts, cache size/TTL, and retry logic with exponential backoff
4. Client Integration:
   - Added cmabService field to OptimizelyClient
   - Added WithCmabService() factory option for dependency injection
   - Modified Decide() method to call CMAB service for CMAB-enabled experiments
5. Decision Enhancement: Extended decision responses to include CMAB predictions alongside existing feature flag results

We need CMAB support for agent in go-sdk because:

1. go-sdk is the core SDK - It contains all the Optimizely decision logic (bucketing, feature flags, etc.)
2. Agent is just a wrapper - Agent creates go-sdk clients and exposes them via HTTP endpoints
3. CMAB integrates with decisions - CMAB predictions need to be combined with existing feature flag logic, which lives in go-sdk's Decide()
   method

This is how CMAB data flows between go-sdk and agent:

1. Client request → Agent's /decide HTTP endpoint
2. Agent → Creates Optimizely client from go-sdk (with CMAB config)
3. go-sdk → Makes prediction API call to CMAB service endpoint
4. CMAB service → Returns ML prediction response
5. go-sdk → Caches prediction + combines with feature flag decision
6. Agent → Returns combined response (feature flags + CMAB predictions) to client

Key points:

• Agent creates the Optimizely client using go-sdk's factory
• go-sdk handles all CMAB API calls, caching, and retry logic
• Agent just passes through the enriched decision response that now includes CMAB data
• The /decide endpoint response format stays the same, just with additional CMAB fields

https://jira.sso.episerver.net/browse/FSSDK-11589