feat: sync Rokt session ID to mParticle via setIntegrationAttribute

[crisryantan]

Summary

Syncs the Rokt session ID back to mParticle so server-side integrations can link mParticle events to Rokt sessions via the Transactions v2 API.

• After selectPlacements() resolves, reads the session ID from selection.context.sessionId
• Subscribes to SESSION_ID_UPDATED events for subsequent session changes
• Calls mParticle.getInstance().setIntegrationAttribute(181, { roktSessionId }) to attach the ID to all future event batches
• Best-effort: early events before session ID arrives will not have the attribute. Wrapped in try/catch to never break the partner page
• Guarded with thenable check so existing callers that don't return a Promise from selectPlacements are unaffected

Testing Plan

• Unit tests: 5 new tests covering happy path, SESSION_ID_UPDATED subscription, empty session ID guard, missing getInstance resilience, and Selection return value preservation
• All 132 existing tests pass (Chrome Headless)
• Manual verification: call selectPlacements(), then check mParticle.getInstance().getIntegrationAttributes(181) returns { roktSessionId: '<session-id>' }
• Verify outbound mParticle event batch contains integration_attributes.181.roktSessionId

🤖 Generated with Claude Code

[alexs-mparticle]

@crisryantan please remove the dist files from your pr

[rmi22186]

@crisryantan Should we also logSelectPlacementsEvent in a catch, and in an else statement? I assume this may happen if a selection fails, in which case we should still send the original selectPlacements event.