chore(*): add mathlib4 synchronization comments (#18057)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebra.gcd_monoid.basic`
* `data.bundle`
* `data.pnat.prime`
* `data.rat.cast`
* `data.set.intervals.monotone`
* `group_theory.group_action.embedding`
* `group_theory.submonoid.center`
* `group_theory.submonoid.centralizer`
* `group_theory.submonoid.operations`
* `group_theory.subsemigroup.membership`
* `order.extension.linear`
* `order.monotone.monovary`
* `order.succ_pred.limit`
