fix: Skip creating `usage_anonymous_id` when TABBY_DISABLE_USAGE_COLLECTION is set (#864)

* dont write file if tracking is disabled

* remove comment, id is optional

* Update usage.rs

---------

Co-authored-by: Meng Zhang <meng@tabbyml.com>

crates/tabby-common/src/usage.rs

@@ -11,7 +11,7 @@ static USAGE_API_ENDPOINT: &str = "https://app.tabbyml.com/api/usage";
 
 struct UsageTracker {
     id: String,
-    client: Option<Client>,
+    client: Client,
 }
 
 impl UsageTracker {
@@ -42,33 +42,28 @@ impl UsageTracker {
         }
 
         let id = fs::read_to_string(usage_id_file()).expect("Failed to read usage id");
-        let client = if std::env::var("TABBY_DISABLE_USAGE_COLLECTION").is_ok() {
-            None
-        } else {
-            Some(Client::new())
-        };
-
-        Self { id, client }
+        Self {
+            id,
+            client: Client::new(),
+        }
     }
 
     async fn capture<T>(&self, event: &str, properties: T)
     where
         T: Serialize,
     {
-        if let Some(client) = &self.client {
         let payload = Payload {
-                distinct_id: self.id.as_ref(),
+            distinct_id: &self.id,
             event,
             properties,
         };
-            client
+        self.client
             .post(USAGE_API_ENDPOINT)
             .json(&payload)
             .send()
             .await
             .ok();
     }
-    }
 }
 
 #[derive(Serialize)]
@@ -80,12 +75,20 @@ struct Payload<'a, T> {
 }
 
 lazy_static! {
-    static ref TRACKER: UsageTracker = UsageTracker::new();
+    static ref TRACKER: Option<UsageTracker> = {
+        if std::env::var("TABBY_DISABLE_USAGE_COLLECTION").is_ok() {
+            None
+        } else {
+            Some(UsageTracker::new())
+        }
+    };
 }
 
 pub async fn capture<T>(event: &str, properties: T)
 where
     T: Serialize,
 {
-    TRACKER.capture(event, properties).await
+    if let Some(tracker) = TRACKER.as_ref() {
+        tracker.capture(event, properties).await;
+    }
 }