feat: add session id to stream events

[varin-nair-factory]

Description

Adds sessionId to SDK stream events by introducing a shared stream base type and threading the SDK-tracked session id through notification conversion and MessageBridge.

Also updates stream/helper/run/integration tests so converted events and result message fixtures account for the new field.

Related Issue

N/A

Potential Risk & Impact

• Additive runtime field on stream events.
• TypeScript consumers constructing stream event objects manually may need to include sessionId.
• Example script fixes were intentionally excluded from this PR per request.

How Has This Been Tested?

• npm run lint
• npm run typecheck
• npm test
• npm run typecheck:examples passed locally only with unstaged example-script fixes, which are not included in this PR.