Split out from mdn_iid_blocks() so the eager driver and the traced one
share a single definition of the density. Everything here depends on the
conditioning variable alone, so it is computed once per call and reused
across every observation chunk.
Split out from mdn_iid_blocks() so the eager driver and the traced one
share a single definition of the density. Everything here depends on the
conditioning variable alone, so it is computed once per call and reused
across every observation chunk.