feat(core): switch to native fetch API for all HTTP requests

ts/bunq.classes.attachment.ts

@@ -47,17 +47,19 @@ export class BunqAttachment {
       'X-Bunq-Client-Authentication': this.bunqAccount.apiContext.getSession().getContext().sessionToken
     };
 
-    const requestOptions = {
-      method: 'PUT' as const,
-      headers: headers,
-      requestBody: options.body
-    };
-
-    await plugins.smartrequest.request(
+    const response = await fetch(
       `${this.bunqAccount.apiContext.getBaseUrl()}${uploadUrl}`,
-      requestOptions
+      {
+        method: 'PUT',
+        headers: headers,
+        body: options.body
+      }
     );
 
+    if (!response.ok) {
+      throw new Error(`Failed to upload attachment: HTTP ${response.status}`);
+    }
+
     return attachmentUuid;
   }
 
@@ -67,7 +69,7 @@ export class BunqAttachment {
   public async getContent(attachmentUuid: string): Promise<Buffer> {
     await this.bunqAccount.apiContext.ensureValidSession();
     
-    const response = await plugins.smartrequest.request(
+    const response = await fetch(
       `${this.bunqAccount.apiContext.getBaseUrl()}/v1/attachment-public/${attachmentUuid}/content`,
       {
         method: 'GET',
@@ -77,7 +79,12 @@ export class BunqAttachment {
       }
     );
 
-    return Buffer.from(response.body);
+    if (!response.ok) {
+      throw new Error(`Failed to get attachment: HTTP ${response.status}`);
+    }
+
+    const arrayBuffer = await response.arrayBuffer();
+    return Buffer.from(arrayBuffer);
   }
 
   /**