language_models: Improve token counting for providers (#32853)

We push the usage data whenever we receive it from the provider to make
sure the counting is correct after the turn has ended.

- [x] Ollama 
- [x] Copilot 
- [x] Mistral 
- [x] OpenRouter 
- [x] LMStudio

Put all the changes into a single PR open to move these to separate PR
if that makes the review and testing easier.

Release Notes:

- N/A

crates/mistral/src/mistral.rs

@@ -379,6 +379,7 @@ pub struct StreamResponse {
     pub created: u64,
     pub model: String,
     pub choices: Vec<StreamChoice>,
+    pub usage: Option<Usage>,
 }
 
 #[derive(Serialize, Deserialize, Debug)]