convert HashFunction to interface

src/commonMain/kotlin/com/infendro/hash/keccak/Keccak.kt

@@ -6,16 +6,11 @@ import com.infendro.bytearray.toULongArray
 import com.infendro.hash.HashFunction
 import kotlin.math.min
 
-open class Keccak(
+abstract class Keccak(
     override val bytes: Int,
     private val rate: Int,
     private val domain: UByte,
-) : HashFunction() {
-    init {
-        if (bytes < 1) throw IllegalArgumentException()
-        if (rate !in 8..168) throw IllegalArgumentException()
-    }
-
+) : HashFunction {
     override val block: Int
         get() = rate
 
@@ -108,7 +103,7 @@ open class Keccak(
         }
     }
 
-    fun squeeze(
+    private fun squeeze(
         state: ULongArray,
     ): UByteArray {
         return buildList {