Module factory 

Engine factory: create engines by ID and list all registered engines.

Functions

create_engine

Create an engine by its string identifier.

engine_count

Return the number of registered engines.

engine_list

Return a list of all registered engine descriptors.

parse_credentials

Parse engine credentials JSON into a string map, coercing JSON scalars (numbers, bools) to their string form. Fixes #58: a single {"numSteps": 16} (JSON number) no longer silently empties ALL credentials — it coerces to "16" like the engine code expects.