sci-mathematics/sympow: new package for symmetric power L-functions.

sci-mathematics/sympow: new package for symmetric power L-functions.

This is an actively-maintained fork of Mark Watkins's original sympow
package (that is now impossible to find) by Debian's Jérôme Benoit.
Sympow is a dependency of SageMath, and SageMath will soon be able to
use the system's copy of sympow. Having this in Gentoo therefore avoids
pointless rebuilds of sympow for Gentoo users of SageMath.

Closes: https://bugs.gentoo.org/230449
Package-Manager: Portage-2.3.99, Repoman-2.3.22
Signed-off-by: Michael Orlitzky <mjo@gentoo.org>