chore(*): add mathlib4 synchronization comments (#19207)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebraic_geometry.open_immersion.basic`
* `analysis.schwartz_space`
* `category_theory.monoidal.internal.types`
* `dynamics.ergodic.add_circle`
* `field_theory.is_alg_closed.algebraic_closure`
* `measure_theory.group.add_circle`
* `measure_theory.integral.periodic`
* `number_theory.kummer_dedekind`
* `number_theory.well_approximable`
* `probability.kernel.integral_comp_prod`
* `probability.martingale.basic`
* `probability.martingale.centering`
* `probability.martingale.optional_sampling`
* `probability.process.hitting_time`
* `ring_theory.is_adjoin_root`
