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

[FarhanAnjum-opti]

Summary

Adds Feature Rollout support to the JavaScript 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 the Experiment interface
• 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
• Added getEveryoneElseVariation helper function to extract the last rollout rule's first variation
• Updated variation lookup maps (variationKeyMap, variationIdMap, variationVariableUsageMap) with injected variation
• Added 6 unit tests covering feature rollout injection, edge cases, and backward compatibility

Jira Ticket

FSSDK-12337

[coveralls]

coverage: 77.728% (-0.005%) from 77.733%
when pulling 27f1621 on ai/farhananjum-opti/FSSDK-12337-feature-rollouts
into cde46e9 on master.