Add support for OpenAI's o1 models by making max_response_tokens optional

The other prerequisite seems to be not using a `prompt` (`prompt: null`),
but we already supported this.

It'd be nice to add an optional `max_completion_tokens` parameter as
well, for the benefit of the o1 models, but this is not yet supported by
async-openai.
Possibly tracked here: https://github.com/64bit/async-openai/issues/272

src/agent/provider/openai_compat/config.rs

@@ -66,7 +66,7 @@ pub struct TextGenerationConfig {
     pub temperature: f32,
 
     #[serde(default)]
-    pub max_response_tokens: u32,
+    pub max_response_tokens: Option<u32>,
 
     #[serde(default)]
     pub max_context_tokens: u32,
@@ -78,7 +78,7 @@ impl Default for TextGenerationConfig {
             model_id: default_text_model_id(),
             prompt: Some(default_prompt().to_owned()),
             temperature: super::super::default_temperature(),
-            max_response_tokens: 4096,
+            max_response_tokens: Some(4096),
             max_context_tokens: 128_000,
         }
     }

src/agent/provider/openai_compat/controller.rs

@@ -131,12 +131,15 @@ impl ControllerTrait for Controller {
 
         let max_tokens = text_generation_config
             .max_response_tokens
-            .try_into()
-            .expect("Failed converting max_response_tokens from u32 to i32");
+            .map(|max_response_tokens| {
+                max_response_tokens
+                    .try_into()
+                    .expect("Failed converting max_response_tokens from u32 to i32")
+            });
 
         let request = ChatBody {
             model: text_generation_config.model_id.clone(),
-            max_tokens: Some(max_tokens),
+            max_tokens,
             temperature: Some(temperature),
             top_p: None,
             n: Some(1),

src/agent/provider/openai_compat/mod.rs

@@ -56,7 +56,7 @@ pub fn default_config() -> Config {
 
     if let Some(text_generation) = &mut config.text_generation {
         text_generation.model_id = "some-model".to_string();
-        text_generation.max_response_tokens = 4096;
+        text_generation.max_response_tokens = Some(4096);
         text_generation.max_context_tokens = 128_000;
     }