feat(set_theory/surreal): add dyadic surreals (#7843)
We define `surreal.dyadic` using a map from \int localized away from 2 to surreals. As currently we do not have the ring structure on `surreal` we do this "by hand".
Next steps:
1. Prove that `dyadic_map` is injective
2. Prove that `dyadic_map` is a group hom
3. Show that \int localized away from 2 is a subgroup of \rat.
