Make BB Session ID public within Stagehand class

[kamath]

why

We should be able to do stagehand.browserbaseSessionId to be able to pull relevant information about the Browserbase session.

what changed

• added sessionId as a public param to Stagehand
• edited getBrowser to return sessionId
• edited associated types
• removed duplicate interface

test plan

• evals CI

[changeset-bot]

🦋 Changeset detected

Latest commit: 9795926

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@browserbasehq/stagehand	Minor

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