Made several attributes of StatementParser immutable

The following attributes within StatementParser were converted from mutable lists to immutable tuples:
- terminators
- multiline_commands
- shortcuts

Author: tleonhardt

cmd2/cmd2.py

@@ -555,7 +555,7 @@ def allow_redirection(self) -> bool:
         return self.statement_parser.allow_redirection
 
     @property
-    def shortcuts(self) -> List[Tuple[str, str]]:
+    def shortcuts(self) -> Tuple[Tuple[str, str]]:
         """Read-only property to access the shortcuts stored in the StatementParser."""
         return self.statement_parser.shortcuts
 

cmd2/parsing.py

@@ -280,21 +280,21 @@ def __init__(
     ):
         self.allow_redirection = allow_redirection
         if terminators is None:
-            self.terminators = [constants.MULTILINE_TERMINATOR]
+            self.terminators = (constants.MULTILINE_TERMINATOR,)
         else:
-            self.terminators = terminators
+            self.terminators = tuple(terminators)
         if multiline_commands is None:
-            self.multiline_commands = []
+            self.multiline_commands = ()
         else:
-            self.multiline_commands = multiline_commands
+            self.multiline_commands = tuple(multiline_commands)
         if aliases is None:
             self.aliases = {}
         else:
             self.aliases = aliases
         if shortcuts is None:
-            self.shortcuts = []
+            self.shortcuts = ()
         else:
-            self.shortcuts = shortcuts
+            self.shortcuts = tuple(shortcuts)
 
         # commands have to be a word, so make a regular expression
         # that matches the first word in the line. This regex has three