Remove low-level interface (breaking)

The main reason the low-level interface exists is to support older compiler, in the case where the "standard json wrapper" is failing. This was a problem until we had testing enabled for multiple versions (#394).

At this point I'd argue that it is more beneficial to fix any potential wrapper issues and just remove the low-level interface.

Start by reviewing the low-level interface and the standard JSON wrapper, then read issue #394 for the multi-version compiler testing context. Done means the low-level interface is removed without leaving unsupported callers, and wrapper behavior remains covered across the compiler versions mentioned in that work.

Written by the indexing model from the issue text.