feat(cmd): add token usage information to commit message prompt

Add code to display the number of tokens used in the commit message prompt.
This information includes the number of tokens used for the prompt and completion,
as well as the total number of tokens used. This helps users understand the
impact of their commit message on token usage.

src/cmd/commit.rs

@@ -87,6 +87,14 @@ impl Run for Cmd {
             .build()
             .log()?;
         let response = client.chat().create(request).await.log()?;
+        if let Some(usage) = response.usage {
+            println!(
+                "Tokens: {} (prompt) + {} (completion) = {} (total)",
+                usage.prompt_tokens.to_string().bold().cyan(),
+                usage.completion_tokens.to_string().bold().cyan(),
+                usage.total_tokens.to_string().bold().cyan()
+            );
+        }
         let select = Select::new(
             &format!(
                 "Pick a commit message to use: {}",