math/kfr: Update to 6.3.1

Backport upstream patches eb615703f5f15eb7794d6ec3f20d83130d9f5274 and
6056e7d24723531e10484d63f6a9a5c58f976daa

Changelog: https://github.com/kfrlib/kfr/releases/tag/6.3.1

References:
https://github.com/kfrlib/kfr/commit/eb615703f5f15eb7794d6ec3f20d83130d9f5274
https://github.com/kfrlib/kfr/commit/6056e7d24723531e10484d63f6a9a5c58f976daa

PR: 289574
Approved by: maintainer timeout, 2+ weeks