fix(cli): fixed regex for parsing flags

Before the RegEx did not contain the starting (^) and ending character ($).

packages/ying-shared/lib/cli/command_execution_context.dart

@@ -4,7 +4,7 @@ import 'package:ying_shared/cli/flag.dart';
 import 'package:ying_shared/utils/stringify.dart';
 
 final flagPattern = RegExp(
-  r"(?<dashes>-{1,2})(?<name>\w+)(=(?<value>.*))?",
+  r"^(?<dashes>-{1,2})(?<name>\w+)(=(?<value>.*))?$",
   dotAll: false,
 );