refactor: Enable derive_default feature & refactor code according it

src/rust/build.rs

@@ -59,6 +59,8 @@ fn main() {
     }
 
     let bindings = builder
+        .derive_default(true)
+        .no_default("dtvcc_pen_attribs|dtvcc_pen_color|dtvcc_symbol")
         // Finish the builder and generate the bindings.
         .generate()
         // Unwrap the Result and panic on failure.

src/rust/src/decoder/mod.rs

@@ -280,3 +280,10 @@ impl dtvcc_symbol {
         is_true(self.init)
     }
 }
+
+impl Default for dtvcc_symbol {
+    /// Create a blank uninitialized symbol
+    fn default() -> Self {
+        Self { sym: 0, init: 0 }
+    }
+}