[AI-FSSDK] [FSSDK-12760] add localHoldouts to datafile for backward compatibility

[jaeopt]

Summary

Adds support for the new top-level localHoldouts datafile section so older SDKs (Gen 1/Gen 2) that don't understand local holdouts safely ignore them while Gen 3 SDKs scope holdouts by section membership.

Changes

• HoldoutConfig — section-aware constructor (globalHoldouts, localHoldouts). Entries in holdouts are global (any includedRules is stripped); entries in localHoldouts must carry includedRules (null/missing → log error + skip; empty list → valid but inert). Legacy single-list constructor preserved as deprecated.
• DatafileProjectConfig — new 21-arg v4 constructor accepting localHoldouts separately. Legacy 20-arg constructor auto-partitions a mixed list by entity-level includedRules for backward compatibility with existing callers.
• All 4 parsers (Gson, Jackson, org.json, json-simple) — read the optional top-level localHoldouts array and pass it through alongside holdouts.
• Holdout — docstring updates clarifying that scope comes from the datafile section, not includedRules.
• Tests — new section-aware tests in HoldoutConfigTest (8 added, 25 total) plus moved the existing local-holdout entry in holdouts-project-config.json into the new localHoldouts section. All existing parser/DecisionService/UserContext tests continue to pass unchanged.

Jira ticket

FSSDK-12760

Reference PRs

• Python: [AI-FSSDK] [FSSDK-12760] Add localHoldouts datafile section for backward compat python-sdk#517
• Ruby: [AI-FSSDK] [FSSDK-12760] Add localHoldouts datafile section ruby-sdk#400

Test plan

• ./gradlew :core-api:test — all suites pass (HoldoutConfigTest: 25/25; all 4 parser tests pass; DecisionServiceTest and OptimizelyUserContextTest pass)
• ./gradlew test — all modules pass
• CI green

[jaeopt]

I reviewed and it looks good to me.