[AI-FSSDK] [FSSDK-12813] Normalize decision event campaign_id, variation_id, and entity_id

[jaeopt]

Summary

Normalize three decision-event fields uniformly across every decision type (experiment, feature test, rollout, holdout) in the event-builder layer so the wire output is byte-equivalent across SDKs for the same input. decisions[].campaign_id and impression events[].entity_id accept any non-empty string (including opaque IDs like "default-12345" or "layer_abc") and fall back to experiment_id only when the value is null or empty string. decisions[].variation_id retains the stricter numeric-string contract and falls back to null for empty / whitespace / non-numeric values. Non-string types are out of scope. Conversion-event entity_id is unchanged. The path never logs, throws, or blocks dispatch.

Changes

• Added OptimizelySDK/Utils/EventIdNormalizer.cs encapsulating the rules with two validators: IsNonEmptyString (for campaign_id / entity_id) and IsNumericIdString (for variation_id). NormalizeCampaignId falls back to experiment_id only when the input is null or ""; NormalizeVariationId falls back to null when the input is not a non-empty decimal-digit string.
• Wired the normalizer into EventFactory.CreateVisitor(ImpressionEvent) and the obsolete EventBuilder.GetImpressionParams so both paths stay byte-equivalent. Impression entity_id reuses the normalized campaign_id.
• Audited existing event-builder tests per FR-011 — happy-path fixtures already use numeric IDs; the rollout case in TestCreateImpressionEventRemovesInvalidAttributesFromPayloadRollout remains correct under the relaxed contract (null LayerId still triggers fallback to empty experiment_id). Unit and integration tests updated for the relaxed campaign_id / entity_id contract: opaque non-empty strings (e.g. "default-12345", "layer_abc", "variation_a") now pass through unchanged; only null and "" trigger the experiment_id fallback. Added IsNonEmptyString unit coverage, an opaque-LayerId pass-through integration test, an empty-LayerId fallback integration test, and a null-LayerId uniform-across-rule-types companion test. variation_id tests are unchanged.

Jira Ticket

FSSDK-12813