[AI-FSSDK] [FSSDK-12369] Add local holdouts support to JavaScript SDK

[Mat001]

Summary

Adds Local Holdouts support to the JavaScript SDK. Local holdouts allow targeting specific experiment or delivery rules within a flag, while global holdouts (the existing behavior) apply to all rules across all flags. This introduces a new rule-level targeting system using an includedRules field on the holdout data model.

Changes

• Added includedRules and isGlobal fields to the Holdout interface in shared_types.ts
• Added HoldoutConfig interface and getGlobalHoldouts / getHoldoutsForRule helper functions to project_config.ts; parseHoldoutsConfig now builds and stores these lookups during config initialization
• Updated decision_service/index.ts to evaluate global holdouts via getGlobalHoldouts() at flag level and check local holdouts per-rule (after forced decisions, before regular rule evaluation) for both experiment rules and delivery rules
• Added Level 1 unit tests for config/parsing (isGlobal classification, backward compat, edge cases) and Level 2 decision service tests (one per branch of the local holdout pseudocode)

Jira Ticket

FSSDK-12369

[coveralls]

coverage: 77.761% (-0.1%) from 77.906% — ai/mat001/FSSDK-12369-local-holdouts into master