feat: support oai completion response usage

src/main/java/ee/carlrobert/llm/client/openai/completion/response/OpenAIChatCompletionResponse.java

@@ -11,13 +11,16 @@ public class OpenAIChatCompletionResponse implements CompletionResponse {
 
   private final String id;
   private final List<OpenAIChatCompletionResponseChoice> choices;
+  private final OpenAIChatCompletionResponseUsage usage;
 
   @JsonCreator(mode = JsonCreator.Mode.PROPERTIES)
   public OpenAIChatCompletionResponse(
       @JsonProperty("id") String id,
-      @JsonProperty("choices") List<OpenAIChatCompletionResponseChoice> choices) {
+      @JsonProperty("choices") List<OpenAIChatCompletionResponseChoice> choices,
+      @JsonProperty("usage") OpenAIChatCompletionResponseUsage usage) {
     this.id = id;
     this.choices = choices;
+    this.usage = usage;
   }
 
   public String getId() {
@@ -27,4 +30,8 @@ public String getId() {
   public List<OpenAIChatCompletionResponseChoice> getChoices() {
     return choices;
   }
+
+  public OpenAIChatCompletionResponseUsage getUsage() {
+    return usage;
+  }
 }

src/main/java/ee/carlrobert/llm/client/openai/completion/response/OpenAIChatCompletionResponseUsage.java

@@ -0,0 +1,35 @@
+package ee.carlrobert.llm.client.openai.completion.response;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+@JsonIgnoreProperties(ignoreUnknown = true)
+public class OpenAIChatCompletionResponseUsage {
+
+  private final int promptTokens;
+  private final int completionTokens;
+  private final int totalTokens;
+
+  @JsonCreator(mode = JsonCreator.Mode.PROPERTIES)
+  public OpenAIChatCompletionResponseUsage(
+      @JsonProperty("prompt_tokens") int promptTokens,
+      @JsonProperty("completion_tokens") int completionTokens,
+      @JsonProperty("total_tokens") int totalTokens) {
+    this.promptTokens = promptTokens;
+    this.completionTokens = completionTokens;
+    this.totalTokens = totalTokens;
+  }
+
+  public int getPromptTokens() {
+    return promptTokens;
+  }
+
+  public int getCompletionTokens() {
+    return completionTokens;
+  }
+
+  public int getTotalTokens() {
+    return totalTokens;
+  }
+}