Using postgres planner as standalone component

Hi,

For one of my personal projects I am interested in using the PostgreSQL
planner as a standalone library. However, I would like to run this as an
embedded library instead of actually creating anything on disk.

I've realized that postgres has several pg_operator, pg_class etc. tables
which it uses for query planning purposes. Is there any PostgreSQL
component interface whose implementation could be overridden to not
actually try to read these tables from disk but instead read it from a
custom memory region that is managed by my code.

Thanks!