feat(ring_theory/polynomial/cyclotomic/*): ɸₙ(1) = 1 (#10483)
(for `n` not a prime power)
Co-authored-by: Eric <37984851+ericrbg@users.noreply.github.com>
Co-authored-by: Yury G. Kudryashov <urkud@urkud.name>
Co-authored-by: Johan Commelin <johan@commelin.net>
