feat: Support CRUD functionality (#7)

The station search implementation only works via DB and is very slow. For a simple query, the answer takes about 1s or longer. That is 100 times slower than it should be. For now, however, this solution is adequate to achieve a first prototype that includes the core functionality.

feat: Add station search

module-common/src/main/kotlin/de/twomartens/timetable/types/Email.kt

@@ -0,0 +1,11 @@
+package de.twomartens.timetable.types
+
+@JvmInline
+value class Email private constructor(val value: String) {
+    companion object {
+        fun of(email: NonEmptyString): Email {
+            require(email.value.contains("@")) { "Invalid email format" }
+            return Email(email.value)
+        }
+    }
+}

module-common/src/main/kotlin/de/twomartens/timetable/types/ZeroOrPositiveInteger.kt

@@ -0,0 +1,10 @@
+package de.twomartens.timetable.types
+
+@JvmInline
+value class ZeroOrPositiveInteger(val value: Int) {
+    init {
+        require(value >= 0) {
+            "Value must be zero or positive integer"
+        }
+    }
+}