mathlib3

10878f6b - feat(linear_algebra/span): generalise to_span_nonzero_singleton (#19082)

feat(linear_algebra/span): generalise to_span_nonzero_singleton (#19082) Co-authored-by: Junyan Xu <junyanxumath@gmail.com> Co-authored-by: Eric Wieser <wieser.eric@gmail.com>