Find RR and RRcell files in directories

[antonleykin]

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Adds `rr_and_rrcell_search_results.md` to document the usage of `RR` and `RRcell` types across the `Macaulay2/d` (frontend) and `Macaulay2/e` (engine) directories. This file summarizes where each type is used and highlights their distinct roles (e.g., `RRcell` being frontend-specific).