mathlib3

8c05ff87 - feat(set_theory/surreal): add ordered_add_comm_group instance for surreal numbers (#7270)

feat(set_theory/surreal): add ordered_add_comm_group instance for surreal numbers (#7270) [Zulip thread](https://leanprover.zulipchat.com/#narrow/stream/116395-maths/topic/Surreal.20numbers/near/235213851) Add ordered_add_comm_group instance for surreal numbers.