Add types to stitch

[mlb2251]

• typecheck at the end. Maybe do it as an assertion because if it failed that might indicate that some of our pruning is pruning wrong. I dont think abstractions should ever mis typecheck
• typecheck the input programs as well ofc
• allow for not giving types as input at all ofc, bc sometimes you might have arbitrary constants or not want to write one or want variadic functions or whatever.
• but when types are provided, it allows you to eta-longify if desired
• types through the json instead of a rust file? idk