Introduce the internal synthesis API

[kiranandcode]

EncodableAs callable should call out to operations compile and eval operations, their default rules should just be to blow up.

[kiranandcode]

In order for a template that returns a callable to not fail, you will need to provide a handler for those operations.

[kiranandcode]

parse
compile
eval

To do the looping handle call_assistant

effectful/effectful/handlers/llm/completions.py

Line 62 in 723e5d9

def call_assistant(