ExplainMicroserviceCost Batch Inference Per Query

[17zhangw]

ExplainMicroserviceCost processes the explain "tree" for a given query and estimates the cost of the query using our models via the microservice. We currently make a network request for each node in the explain tree.

The overall goals of this task to restructure ExplainMicroserviceCost is as follows:

1. Insert some tooling/instrumentation to extract microservice inference times (can also be logged to sqlite)
2. Make 1 network call to perform model inference for an entire query explain tree
3. Allow for partial query explain tree cost inference (i.e., failing 1 node does not fail the entire tree)
4. Batch logging the inference + real query results

[lmwnshn]

Forgot that we need to manually close things if we don't tag it as Fix...