ensure const arrays in Polyval cache
ensure const arrays in Polyval cache

The arguments of `Polyval.eval` are not guaranteed to be `numeric.const`.  The
caching system, however, requires hashable arguments.  We now convert ordinary
`numpy.ndarray` objects to `numeric.const` before calling the cache.

CVerhoosel/nutils,nutils/nutils,joostvanzwieten/nutils,wijnandhoitinga/nutils