Adds a flatten to set utility

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip01Core/tags/hashtags/MipMapHashTags.kt

@@ -20,6 +20,8 @@
  */
 package com.vitorpamplona.quartz.nip01Core.tags.hashtags
 
+import com.vitorpamplona.quartz.utils.flattenToSet
+
 fun hashtagAlts(tag: String): Set<String> =
     setOf(
         tag,
@@ -30,6 +32,6 @@ fun hashtagAlts(tag: String): Set<String> =
         },
     )
 
-fun hashtagAlts(tags: List<String>): Set<String> = tags.map { hashtagAlts(it) }.flatten().toSet()
+fun hashtagAlts(tags: List<String>): Set<String> = tags.map { hashtagAlts(it) }.flattenToSet()
 
-fun hashtagAlts(tags: Set<String>): Set<String> = tags.map { hashtagAlts(it) }.flatten().toSet()
+fun hashtagAlts(tags: Set<String>): Set<String> = tags.map { hashtagAlts(it) }.flattenToSet()

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/utils/IterableExt.kt

@@ -46,3 +46,11 @@ fun <T> Iterable<T>.joinToStringLimited(
     buffer.append(postfix)
     return buffer.toString()
 }
+
+public fun <T> Iterable<Iterable<T>>.flattenToSet(): Set<T> {
+    val result = mutableSetOf<T>()
+    for (element in this) {
+        result.addAll(element)
+    }
+    return result
+}