fix(engine): Index UserSessions columns for cleanup

[gregfurman]

Description

Ensures that the expiredAt and createdAt columns are correctly indexed -- addressing failing UserSession cleanup jobs that were introduced in the last stable release.

Type of change

• Bug fix (non-breaking change which fixes an issue)

What's Changed

• Added migration to index createdAt and expiresAt columns in UserSessions table.

Checklist

Changes have been:

• Tested (unit, integration, or manually with steps specified)
• Linted and formatted
• Documented (where applicable)
• Added to CHANGELOG (where applicable) -- see Keep a Changelog

---

🤖 AI Disclosure

• I acknowledge that an LLM was used in the creation of this Pull Request, in accordance with Hatchet's AI_POLICY.md.

• Details: [e.g. generating tests, writing docs]

[vercel]

@gregfurman is attempting to deploy a commit to the Hatchet Team on Vercel.

A member of the Team first needs to authorize it.

[gregfurman]

Needs docs regen 😬 Will do so a bit later