[FSSDK-11169] Implement Decision Service methods to handle CMAB

[Mat001]

Decision Service methods to handle CMAB

• added experiment_cmab_service.go file with cmab supportig methods
• additionally updated decision/entities.go and decision/reasons/reason.go

Added unit tests.

Jira ticket: https://jira.sso.episerver.net/browse/FSSDK-11169

[Copilot]

Pull Request Overview

This PR implements support for CMAB decision making in the Decision Service by adding new CMAB methods, updating relevant entities and reasons, and integrating the CMAB service into the composite experiment service.

• Added experiment_cmab_service.go with CMAB-related decision logic
• Updated reason constants and entities to include CMAB support
• Integrated CMAB decision service in the composite experiment service and added corresponding unit tests

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pkg/decision/reasons/reason.go	Added new constant CmabVariationAssigned for CMAB decisions
pkg/decision/experiment_cmab_service_test.go	Introduced unit tests for various CMAB decision scenarios
pkg/decision/experiment_cmab_service.go	Implemented the CMAB decision logic and error handling
pkg/decision/entities.go	Updated entities to register the new Cmab Source
pkg/decision/composite_experiment_service.go	Extended composite service to include CMAB service integration

Comments suppressed due to low confidence (1)

pkg/decision/reasons/reason.go:63

• [nitpick] The string value for CmabVariationAssigned is inconsistent with the format of other reason constants. Consider using a consistent, human-readable format (e.g. "CMAB variation assigned") to improve clarity.

CmabVariationAssigned Reason = "cmab_variation_assigned"