chore(*): add mathlib4 synchronization comments (#18595)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebra.algebra.subalgebra.pointwise`
* `algebra.algebra.unitization`
* `algebra.char_p.exp_char`
* `algebra.direct_sum.module`
* `algebra.field.ulift`
* `algebra.monoid_algebra.degree`
* `algebra.monoid_algebra.no_zero_divisors`
* `algebra.triv_sq_zero_ext`
* `category_theory.category.Bipointed`
* `category_theory.concrete_category.bundled_hom`
* `category_theory.elementwise`
* `category_theory.preadditive.of_biproducts`
* `data.complex.exponential`
* `data.mv_polynomial.basic`
* `data.mv_polynomial.comap`
* `data.mv_polynomial.counit`
* `data.mv_polynomial.rename`
* `data.polynomial.cancel_leads`
* `data.polynomial.identities`
* `group_theory.perm.cycle.basic`
* `measure_theory.card_measurable_space`
* `ring_theory.algebra_tower`
* `ring_theory.coprime.ideal`
* `ring_theory.free_ring`
* `ring_theory.ideal.prod`
* `ring_theory.mv_polynomial.tower`
* `ring_theory.polynomial.opposites`
* `ring_theory.subring.pointwise`
* `ring_theory.valuation.basic`
* `topology.algebra.nonarchimedean.basic`
* `topology.algebra.open_subgroup`
* `topology.algebra.with_zero_topology`
* `topology.homotopy.equiv`
