mathlib

a3f589c0 - feat(analysis/calculus/deriv): `has_deriv_at.continuous_on` (#7260)

feat(analysis/calculus/deriv): `has_deriv_at.continuous_on` (#7260) See [Zulip](https://leanprover.zulipchat.com/#narrow/stream/116395-maths/topic/has_deriv_at.2Econtinuous_on/near/235034547).