Function find_schema 

pub fn find_schema<'a>(
    engine: &'a Engine,
    sref: &SchemaRef,
) -> Option<&'a Arc<Schema>>

Find a schema in the unified engine’s catalogue matching the given memstead_schema::SchemaRef. Mem-pinned first, then workspace, then built-ins. Mirrors memstead_mem_create’s resolution order so memstead_schema(name=<ref>) resolves any pin memstead_mem_create would accept — built-in, workspace-pinned, or mem-pinned.