chore(*): add mathlib4 synchronization comments (#19032)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebra.direct_sum.algebra`
* `algebra.direct_sum.ring`
* `algebra.homology.opposite`
* `algebra.homology.quasi_iso`
* `algebraic_topology.fundamental_groupoid.basic`
* `analysis.box_integral.partition.subbox_induction`
* `analysis.complex.circle`
* `analysis.normed_space.is_R_or_C`
* `analysis.normed_space.operator_norm`
* `analysis.special_functions.trigonometric.angle`
* `analysis.special_functions.trigonometric.basic`
* `analysis.special_functions.trigonometric.inverse`
* `category_theory.limits.constructions.over.products`
* `category_theory.preadditive.endo_functor`
* `combinatorics.simple_graph.ends.properties`
* `combinatorics.simple_graph.finsubgraph`
* `linear_algebra.multilinear.finite_dimensional`
* `ring_theory.free_comm_ring`
* `ring_theory.polynomial.quotient`
* `ring_theory.tensor_product`
* `topology.algebra.module.finite_dimension`
* `topology.metric_space.partition_of_unity`
