chore(*): add mathlib4 synchronization comments (#18319)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebra.graded_monoid`
* `algebra.module.equiv`
* `algebra.module.opposites`
* `algebra.module.submodule.basic`
* `data.dfinsupp.basic`
* `data.enat.lattice`
* `data.finsupp.defs`
* `data.finsupp.order`
* `data.int.interval`
* `data.list.cycle`
* `data.nat.hyperoperation`
* `data.sym.sym2`
* `deprecated.subgroup`
* `dynamics.periodic_pts`
* `group_theory.free_group`
* `group_theory.group_action.conj_act`
* `group_theory.group_action.fixing_subgroup`
* `group_theory.group_action.sub_mul_action`
* `group_theory.is_free_group`
* `group_theory.perm.list`
* `group_theory.subgroup.saturated`
* `group_theory.subgroup.simple`
* `ring_theory.ring_invo`
* `topology.bornology.hom`
* `topology.locally_finite`
* `topology.nhds_set`
