[AI-FSSDK] [FSSDK-12337] Add Feature Rollout support

[FarhanAnjum-opti]

Summary

Adds Feature Rollout support to the Go SDK. Feature Rollouts are a new experiment rule type that combines Targeted Delivery simplicity with A/B test measurement capabilities. During project config parsing, the "everyone else" variation from the flag's rollout is injected into any experiment with type "feature_rollout", enabling correct evaluation without changes to decision logic.

Changes

• Added optional Type string field to both the datafile entity and SDK Experiment entity
• Added config parsing logic to inject the "everyone else" rollout variation into feature_rollout experiments
• Added traffic allocation entry (endOfRange=10000) for the injected variation
• Updated variation lookup maps (Variations, VariationKeyToIDMap) with injected variation
• Added 6 unit tests covering feature rollout injection, edge cases, and backward compatibility

Jira Ticket

FSSDK-12337

[Mat001]

@FarhanAnjum-opti I would perhaps (optionally) add a test for invalid experiment type:

func TestInvalidExperimentTypeReturnsError(t *testing.T) {
// Test that datafile with type="unknown_type" returns error
}