Trace saving migration (#309)

* first steps

* queue everything for now

* added better saving mechanism

* added new endpoints

* langgraph WIP fixes

* add assert test fixes

* fix tests

* small cleanup modification

* some tests code

* fix the timing

* add blocking on shutdown + fix timing

* fix langgraph cost tracking + remove not necessary spans call

* resolve comments

* fix some bugs with latency

* s3 fixes

Author: Mandolaro