Extract the pure prefix-matcher off @Singleton FirmSuggestionCache into utils/Suggestions

FirmSuggestionCache (a @Singleton stateful cache) carried a pure static match(pool, prefix, limit) prefix-filter used by 3 command-parameter resolvers — a generic mechanism living as a static on a stateful service (the same "static-on-a-service" smell cleaned in ChestShop).

Fix: move match to a pure utils/Suggestions; the 3 resolvers call Suggestions.match; the cache keeps only its instance cache methods. The 4 match unit tests move to SuggestionsTest. Coverage-neutral.