Does divorce take effect through obsessive doubts and the repetition of words within one's mind without intending to utter them, or by moving the tongue without sound, or by uttering them with the intention of studying and reviewing, not of initiating a divorce? And does a revocable return (rajʿah) take effect if a person utters it as a precaution, and then it becomes clear that the divorce did not take place?

It appears you are afflicted with waswasah (obsessive whispering/doubts), and you must strive against yourself to overcome it. Everything you mentioned in your message falls under the category of waswasah, which does not result in divorce and does not affect the marriage contract. It is mentioned in the books of the Maliki school that a person afflicted with waswasah is not bound by divorce, and that this comes from Satan, so one should disregard it. Furthermore, recounting or mentioning divorce for the purpose of study or learning does not have any consequences. You are not required to utter the words of raj'ah (returning to one's wife after a revocable divorce) as a precaution; rather, this is a blameworthy form of excessive strictness (tanattu'). And even if you were to utter them, they would be futile and without effect.