Avoid BoxesRuntime indirection in LruBoundedCache key comparison (#31356)

By restricting the key type of `LruBoundedCache` to `AnyRef`, we can
avoid the indirection through `BoxesRuntime`, we remove some overhead
and potentially unlock some JVM optimizations here.

akka-remote/src/main/scala/akka/remote/artery/LruBoundedCache.scala

@@ -23,7 +23,7 @@ private[akka] case class CacheStatistics(entries: Int, maxProbeDistance: Int, av
  * to kick out entires that are considered old. The implementation tries to keep the map close to full, only evicting
  * old entries when needed.
  */
-private[akka] abstract class LruBoundedCache[K: ClassTag, V <: AnyRef: ClassTag](
+private[akka] abstract class LruBoundedCache[K <: AnyRef: ClassTag, V <: AnyRef: ClassTag](
     capacity: Int,
     evictAgeThreshold: Int) {
   require(capacity > 0, "Capacity must be larger than zero")