chore(*): add mathlib4 synchronization comments (#18984)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebra.category.Group.epi_mono`
* `algebra.category.Group.equivalence_Group_AddGroup`
* `algebra.continued_fractions.computation.correctness_terminating`
* `analysis.convex.partition_of_unity`
* `analysis.normed.group.controlled_closure`
* `analysis.normed_space.compact_operator`
* `category_theory.abelian.pseudoelements`
* `category_theory.preadditive.hom_orthogonal`
* `category_theory.sites.cover_preserving`
* `computability.halting`
* `computability.partrec_code`
* `dynamics.ergodic.ergodic`
* `dynamics.ergodic.measure_preserving`
* `measure_theory.covering.vitali_family`
* `measure_theory.decomposition.unsigned_hahn`
* `measure_theory.group.arithmetic`
* `measure_theory.lattice`
* `measure_theory.measure.mutually_singular`
* `measure_theory.measure.open_pos`
* `probability.conditional_probability`
* `topology.algebra.equicontinuity`
* `topology.category.Profinite.as_limit`
* `topology.category.Top.limits.products`
* `topology.continuous_function.locally_constant`
