Add distinct error types

ballerina/error.bal

@@ -16,3 +16,23 @@
 
 # Defines the common error type for the module.
 public type Error distinct error;
+
+# Represents an error that occurs when connecting to the FTP/SFTP server.
+# This includes network failures, host unreachable, connection refused, etc.
+public type ConnectionError distinct Error;
+
+# Represents an error that occurs when a requested file or directory is not found.
+public type FileNotFoundError distinct Error;
+
+# Represents an error that occurs when attempting to create a file or directory that already exists.
+public type FileAlreadyExistsError distinct Error;
+
+# Represents an error that occurs when FTP/SFTP configuration is invalid.
+# This includes invalid port numbers, invalid regex patterns, invalid timeout values, etc.
+public type InvalidConfigurationError distinct Error;
+
+# Represents an error that occurs when the FTP/SFTP service is temporarily unavailable.
+# This is a transient error indicating the operation may succeed on retry.
+# Common causes include: server overload (421), connection issues (425, 426),
+# temporary file locks (450), or server-side processing errors (451).
+public type ServiceUnavailableError distinct Error;

ballerina/tests/advanced_file_selection_test.bal

@@ -65,7 +65,7 @@ function testFileAgeFilterRespectsMaxAge() returns error? {
             }
         },
         path: "/home/in/advanced/age",
-        pollingInterval: 5,
+        pollingInterval: 2,
         fileAgeFilter: {
             maxAge: 60
         },