fix: ScreenshotCachePayload serialization

[betodealmeida]

SUMMARY

Change the serialization of ScreenshotCachePayload, since it doesn't work across all cache backends. The new implementation serializes the object into a dictionary of attributes.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[korbit-ai]

Based on your review schedule, I'll hold off on reviewing this PR until it's marked as ready for review. If you'd like me to take a look now, comment /korbit-review.

Your admin can change your review schedule in the Korbit Console

[sadpandajoe]

@michael-s-molina would be good if we can cherry this in also for part of 5.0rc2