Commit 2026-03-20 06:03 512183e4

chore(Algebra/CharP/MixedCharZero): cleanup file and use module system (#34676)

• mark all internal declarations in the file as private
• remove @[exposed] from the public section
• reduce public imports
• use theorem and lemma to highlight main results. This got lost in the port but was present in mathlib3.
• fix some wording and drop a random example which shouldn't be there