feat: wrappers and debugging get/set for the closed groups in user groups

libsignal/src/main/java/org/session/libsignal/utilities/SessionId.kt

@@ -0,0 +1,27 @@
+package org.session.libsignal.utilities
+
+class SessionId {
+
+    companion object {
+        // needed because JNI doesn't want to detect alternate constructors :shrug:
+        @JvmStatic
+        fun from(id: String): SessionId = SessionId(id)
+    }
+
+    var prefix: IdPrefix?
+    var publicKey: String
+
+    constructor(id: String) {
+        prefix = IdPrefix.fromValue(id)
+        publicKey = id.drop(2)
+    }
+
+    constructor(prefix: IdPrefix, publicKey: ByteArray) {
+        this.prefix = prefix
+        this.publicKey = publicKey.toHexString()
+    }
+
+    fun hexString() = prefix?.value + publicKey
+
+    fun bytes(): ByteArray = Hex.fromStringCondensed(prefix?.value + publicKey)
+}