fix: resolve #828 by updating websocket's thread id header with currentThreadId to ensure session continuation after backend restart

[qtangs]

Resolve #828 by updating websocket's thread id header with currentThreadId to ensure session continuation after backend restart #996

Changes:

• Update websocket headers to use currentThreadId when it's updated
• Modify data_layer test to save thread history for reload after backend restarts
• Add new test to ensure the thread is resumed properly with correct state and also ensure that new threads after restart work as before.

[willydouhard]

This looks really nice, will run a couple more tests before merging. Thank you for your contribution!