[AI-FSSDK] [FSSDK-12369] Add local holdouts support (includedRules, per-rule evaluation)

[Mat001]

Summary

This PR adds Local Holdouts support to the Go SDK. Local holdouts target specific experiment or delivery rules within a flag (via includedRules), while global holdouts (with includedRules == nil) continue to apply to all rules across all flags as before.

Changes

• Add optional IncludedRules []string field to the datafile and SDK Holdout entity; add IsGlobal() computed method
• Update MapHoldouts to build a ruleHoldoutsMap for local holdouts alongside the existing flagHoldoutsMap for global holdouts
• Add GetGlobalHoldouts() and GetHoldoutsForRule(ruleID) to ProjectConfig interface and implementation
• Add EvaluateLocalHoldouts to HoldoutService and wire it into FeatureExperimentService and RolloutService for per-rule evaluation before forced decisions
• Old datafiles without includedRules parse correctly as global holdouts (backward compatible)

Jira Ticket

FSSDK-12369

[Mat001]

Closing as part of cleanup for FSSDK-12369.