message: add impl Send for boxed types
diff: @@ -2045,6 +2045,8 @@ class VectorTypeInfo(TypeInfo):
  ${vector_methods}}
  + unsafe impl Send for ${rust_local} {}
  +
  """),
  "rust_methods_boxed": template("""
  @@ -2327,6 +2329,9 @@ class SmartPtrTypeInfo(TypeInfo):
  })
  }
  }
  +
  + unsafe impl Send for ${rust_local} {}
  +
  """),
  "rust_trait_cast": template("""
  @@ -2968,10 +2973,10 @@ class RustWrapperGenerator(object):
  self.moduleSafeRust.write("// boxed class %s\n"%(typ.typeid))
  self.moduleSafeRust.write(self.reformat_doc(ci.comment))
  self.moduleSafeRust.write(template("""
  - #[allow(dead_code)]
  - pub struct $rust_local {
  + pub struct ${rust_local} {
  #[doc(hidden)] pub(crate) ptr: *mut c_void
  }
  +
  impl Drop for $rust_full {
  fn drop(&mut self) {
  unsafe { sys::cv_${rust_local}_delete(self.ptr) };
  @@ -2985,6 +2990,8 @@ class RustWrapperGenerator(object):
  }
  }
  + unsafe impl Send for ${rust_local} {}
  +
  """).substitute(typ.__dict__))
  for base in sorted(self.all_bases(name)):
  