Searchable Events — the NIP-50 indexing surface

The contract

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip50Search/SearchableEvent.kt:

interface SearchableEvent {
    fun indexableContent(): String
}

One method; marker and extractor in one. An event kind is searchable iff its event class implements this interface and the class is wired into EventFactory (the stores probe searchability by kind through EventFactory.create — an unwired implementor is invisible).

Rules every implementation follows (keep them when adding one):