fix: preserve I/O exception constructor ABI

Author: sylvesterkaczmarek

openai-java-core/src/main/kotlin/com/openai/errors/OpenAIIoException.kt

@@ -5,11 +5,13 @@ import java.util.Optional
 
 class OpenAIIoException
 @JvmOverloads
-constructor(
-    message: String? = null,
-    cause: Throwable? = null,
-    private val headers: Headers? = null,
-) : OpenAIException(message, cause) {
+constructor(message: String? = null, cause: Throwable? = null) : OpenAIException(message, cause) {
 
-    fun headers(): Optional<Headers> = Optional.ofNullable(headers)
+    private var responseHeaders: Headers? = null
+
+    internal constructor(message: String?, cause: Throwable?, headers: Headers) : this(message, cause) {
+        responseHeaders = headers
+    }
+
+    fun headers(): Optional<Headers> = Optional.ofNullable(responseHeaders)
 }