chore: add zone concepts

Author: AndreaGiulianelli

src/main/kotlin/entity/zone/Zone.kt

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2023. Smart Operating Block
+ *
+ * Use of this source code is governed by an MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT.
+ */
+
+package entity.zone
+
+/**
+ * It describes a zone inside the Operating block.
+ * Each zone is identified by an [id] and described
+ * by a [name] and a [description].
+ */
+data class Zone(
+    val id: ZoneID,
+    val name: String,
+    val description: String,
+) {
+    init {
+        require(this.name.isNotEmpty())
+        require(this.description.isNotEmpty())
+    }
+
+    override fun equals(other: Any?): Boolean = when {
+        other === this -> true
+        other is Zone -> this.id == other.id
+        else -> false
+    }
+
+    override fun hashCode(): Int = this.id.hashCode()
+}
+
+/**
+ * It represents the Operating Block zone ID [value].
+ */
+data class ZoneID(val value: String) {
+    init {
+        // Constructor validation: the id must not be empty
+        require(this.value.isNotEmpty())
+    }
+}