Refactor downloaders to use generic options and unify logic

Replaces specialized binary and HTML downloaders with a generic, options-driven UnitDownloader and UnitFragmentDownloader pattern. Introduces UnitDownloaderOptions and builder classes for flexible configuration, updates interfaces and method signatures to support progress reporting, and removes redundant binary-specific classes. Updates Playwright and Stealth downloaders to use the new generic base, and adds improved error handling and reporting. Also updates dependency versions and makes minor API consistency improvements across the Fluent and Models layers.

Beam.Exceptions/Exceptions.Designer.cs

@@ -157,5 +157,32 @@ namespace Beam.Exceptions {
                 return ResourceManager.GetString("state_change_error", resourceCulture);
             }
         }
+        
+        /// <summary>
+        ///   Looks up a localized string similar to Could not open a filestream to a non-existant directory &apos;{0}&apos;..
+        /// </summary>
+        public static string unit_download_directory_nonexistant {
+            get {
+                return ResourceManager.GetString("unit_download_directory_nonexistant", resourceCulture);
+            }
+        }
+        
+        /// <summary>
+        ///   Looks up a localized string similar to The memory stream was created with an invisible inner byte array..
+        /// </summary>
+        public static string unit_download_invalid_memory_stream {
+            get {
+                return ResourceManager.GetString("unit_download_invalid_memory_stream", resourceCulture);
+            }
+        }
+        
+        /// <summary>
+        ///   Looks up a localized string similar to The base unit downloader class only supports RawType&apos;s of string and ByteDocument..
+        /// </summary>
+        public static string unit_downloader_limited_support {
+            get {
+                return ResourceManager.GetString("unit_downloader_limited_support", resourceCulture);
+            }
+        }
     }
 }