feat(messages): add assistant tools to attachements (#370)

openai-core/src/commonMain/kotlin/com.aallam.openai.api/message/Attachment.kt

@@ -1,5 +1,7 @@
 package com.aallam.openai.api.message
 
+import com.aallam.openai.api.BetaOpenAI
+import com.aallam.openai.api.assistant.AssistantTool
 import com.aallam.openai.api.file.FileId
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
@@ -8,9 +10,42 @@ import kotlinx.serialization.Serializable
  * References an Attachment in the message request.
  */
 @Serializable
+@OptIn(BetaOpenAI::class)
 public data class Attachment(
     /**
      * The ID of the file to attach to the message.
      */
-    @SerialName("file_id") val fileId: FileId
+    @SerialName("file_id") val fileId: FileId? = null,
+
+    /**
+     * The tools to add this file to.
+     */
+    @SerialName("tools") val tools: List<AssistantTool>? = null,
 )
+
+/**
+ * A message attachment builder.
+ */
+public fun attachment(block: AttachmentBuilder.() -> Unit): Attachment = AttachmentBuilder().apply(block).build()
+
+/**
+ * A message attachment builder.
+ */
+public class AttachmentBuilder {
+    /**
+     * The ID of the file to attach to the message.
+     */
+    public var fileId: FileId? = null
+
+    /**
+     * The tools to add this file to.
+     */
+    @OptIn(BetaOpenAI::class)
+    public var tools: List<AssistantTool>? = null
+
+    /**
+     * Build the attachment.
+     */
+    @OptIn(BetaOpenAI::class)
+    public fun build(): Attachment = Attachment(fileId, tools)
+}