fix(chat): JsonSchema strict to be encoded even if it's default value is true (#430)

* fix JsonSchema strict not being encoded to json

* fix test additionalProperties required to be false when strict true

Author: LittleTrickster

openai-client/src/commonTest/kotlin/com/aallam/openai/client/TestChatCompletions.kt

@@ -152,7 +152,8 @@ class TestChatCompletions : TestOpenAI() {
             "required" to JsonArray(listOf(
                 JsonPrimitive("question"),
                 JsonPrimitive("response")
-            ))
+            )),
+            "additionalProperties" to JsonPrimitive(false)
         ))
 
         val jsonSchema = JsonSchema(

openai-core/src/commonMain/kotlin/com.aallam.openai.api/chat/ChatResponseFormat.kt

@@ -56,5 +56,5 @@ public data class JsonSchema(
     /**
      * Whether to enforce strict schema validation
      */
-    @SerialName("strict") val strict: Boolean = true
+    @SerialName("strict") val strict: Boolean? = null
 )