refactor: partially migrate to singleton pattern

src-tauri/src/api_client.rs

@@ -315,7 +315,7 @@ pub struct ApiClient {
 }
 
 impl ApiClient {
-  pub fn new() -> Self {
+  fn new() -> Self {
     Self {
       client: Client::new(),
       firefox_api_base: "https://product-details.mozilla.org/1.0".to_string(),
@@ -327,6 +327,10 @@ impl ApiClient {
     }
   }
 
+  pub fn instance() -> &'static ApiClient {
+    &API_CLIENT
+  }
+
   #[cfg(test)]
   pub fn new_with_base_urls(
     firefox_api_base: String,
@@ -1336,6 +1340,11 @@ impl ApiClient {
   }
 }
 
+// Global singleton instance
+lazy_static::lazy_static! {
+  static ref API_CLIENT: ApiClient = ApiClient::new();
+}
+
 #[cfg(test)]
 mod tests {
   use super::*;