Add support to pack xp3 files

src/scripts/base.rs

@@ -586,6 +586,11 @@ pub trait Script: std::fmt::Debug + std::any::Any {
 pub trait Archive {
     /// Creates a new file in the archive.
     fn new_file<'a>(&'a mut self, name: &str) -> Result<Box<dyn WriteSeek + 'a>>;
+    /// Creates a new file in the archive that does not require seeking.
+    fn new_file_non_seek<'a>(&'a mut self, name: &str) -> Result<Box<dyn Write + 'a>> {
+        self.new_file(name)
+            .map(|f| Box::new(f) as Box<dyn Write + 'a>)
+    }
     /// Writes the header of the archive. (Must be called after writing all files.)
     fn write_header(&mut self) -> Result<()>;
 }