Refactor file handling and dataset file listing logic

Improves file picker logic to allow single file selection from multiple paths and refactors dataset file listing to remove redundant empty checks. This streamlines error handling and simplifies code paths.

Author: JR-1991

src/cli/file_picker.rs

@@ -99,8 +99,11 @@ impl Into<UploadFile> for FilePickerResult {
     fn into(self) -> UploadFile {
         match self {
             FilePickerResult::Single(path) => UploadFile::from(path),
-            FilePickerResult::Multiple(_) => {
-                panic!("Multiple files are not supported for this operation.");
+            FilePickerResult::Multiple(paths) => {
+                if paths.len() > 1 {
+                    panic!("Multiple files are not supported for this operation.");
+                }
+                UploadFile::from(paths[0].clone())
             }
         }
     }

src/native_api/dataset/listfiles.rs

@@ -59,18 +59,8 @@ pub async fn list_dataset_files(
         .ok_or("No data found in dataset metadata".to_string())?;
 
     let files = match dataset.latest_version {
-        Some(latest_version) => {
-            if latest_version.files.is_empty() {
-                return Err("No files found in dataset".to_string());
-            }
-            latest_version.files
-        }
-        None => {
-            if dataset.files.is_empty() {
-                return Err("No files found in dataset".to_string());
-            }
-            dataset.files
-        }
+        Some(latest_version) => latest_version.files,
+        None => dataset.files,
     };
 
     let files = files