fix: add scala-parallel-collections for Scala 2.12 compatibility

The CollectionConverters import requires scala-parallel-collections
library for both Scala 2.12 and 2.13. Added version 0.2.0 for 2.12
and kept 1.0.4 for 2.13.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: derrickburns

build.sbt

@@ -27,9 +27,11 @@
       "org.scalacheck" %% "scalacheck" % "1.17.0" % "test"
     )
 
-    // Scala 2.13 requires parallel collections as a separate dependency
+    // Both Scala 2.12 and 2.13 need parallel collections library for CollectionConverters
     libraryDependencies ++= {
       CrossVersion.partialVersion(scalaVersion.value) match {
+        case Some((2, 12)) =>
+          Seq("org.scala-lang.modules" %% "scala-parallel-collections" % "0.2.0")
         case Some((2, n)) if n >= 13 =>
           Seq("org.scala-lang.modules" %% "scala-parallel-collections" % "1.0.4")
         case _ =>

src/main/scala/com/massivedatascience/clusterer/KMeansPlusPlus.scala

@@ -24,6 +24,8 @@ import com.massivedatascience.util.XORShiftRandom
 
 import scala.annotation.tailrec
 import scala.collection.mutable.ArrayBuffer
+
+// Cross-version compatible parallel collections import
 import scala.collection.parallel.CollectionConverters._
 
 /** This implements the <a href="http://ilpubs.stanford.edu:8090/778/1/2006-13.pdf">KMeans++ initialization