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

[Mat001]

Summary

Adds local holdouts support to the Python SDK. Local holdouts target specific experiment/delivery rules (via a new includedRules field) while global holdouts continue to apply to all rules across all flags. This implements rule-level holdout evaluation as described in the FSSDK-12369 spec.

Changes

• Add includedRules field and is_global computed property to the Holdout entity in entities.py
• Add global_holdouts list and rule_holdouts_map dict to ProjectConfig, with get_global_holdouts() and get_holdouts_for_rule() methods
• Update decision_service.py to evaluate global holdouts at flag level and check local holdouts per-rule before audience/traffic allocation
• Add includedRules to HoldoutDict type in types.py
• Add 19 unit tests covering data model, mapping logic, decision flow, backward compatibility, and edge cases

Jira Ticket

FSSDK-12369