Consider rewriting NaturalEarth shapefiles as flatgeobuf
MapServer 8.0 is adding support for flatgeobuf files which show a decent improvement in speed. Since we already need to look at rewriting some of the shapes because of https://gitlab.ssec.wisc.edu/cspp_geo/geosphere/cspp-geo-web-viewer/-/issues/58, this may be a good opportunity.
https://mapserver.org/development/rfc/ms-rfc-137.html#rfc137