✨ feat(StringOrDefault): add toString method to handle nullable values

- implement toString method to return DEFAULT_MARKER for null values

Author: twisti-dev

surf-api-core/surf-api-core/src/main/kotlin/dev/slne/surf/api/core/config/type/StringOrDefault.kt

@@ -27,6 +27,10 @@ data class StringOrDefault private constructor(val value: String?) {
 
     infix fun or(default: String): String = value ?: default
 
+    override fun toString(): String {
+        return value ?: DEFAULT_MARKER
+    }
+
     companion object {
         private const val DEFAULT_MARKER = "__default__"