Depth: Add fun value() to get the raw value

wot-dijkstra/src/main/kotlin/org/pgpainless/wot/dijkstra/sq/Depth.kt

@@ -49,6 +49,15 @@ class Depth private constructor(val limit: Int?) : Comparable<Depth> {
         return limit == null
     }
 
+    /**
+     * The value of this Depth, as used in OpenPGP.
+     *
+     * Unlimited is 255.
+     */
+    fun value(): Int {
+        return limit ?: 255
+    }
+
     /**
      * Decrease the trust depth by one and return the result.
      * If the [Depth] is unconstrained, the result will still be unconstrained.