Batch 2: Add data_length implementations (#554)

- Add data_length to Implicit<T, {TAG}>
- Add data_length to &T (reference to SimpleAsn1Writable type)
- Add data_length to Box<T> (boxed SimpleAsn1Writable type)

Author: alex

src/types.rs

@@ -152,13 +152,21 @@ impl<T: SimpleAsn1Writable> SimpleAsn1Writable for &T {
     fn write_data(&self, dest: &mut WriteBuf) -> WriteResult {
         T::write_data(self, dest)
     }
+
+    fn data_length(&self) -> Option<usize> {
+        T::data_length(self)
+    }
 }
 
 impl<T: SimpleAsn1Writable> SimpleAsn1Writable for Box<T> {
     const TAG: Tag = T::TAG;
     fn write_data(&self, dest: &mut WriteBuf) -> WriteResult {
         T::write_data(self, dest)
     }
+
+    fn data_length(&self) -> Option<usize> {
+        T::data_length(self)
+    }
 }
 
 /// A TLV (type, length, value) represented as the tag and bytes content.
@@ -1955,6 +1963,10 @@ impl<T: SimpleAsn1Writable, const TAG: u32> SimpleAsn1Writable for Implicit<T, {
     fn write_data(&self, dest: &mut WriteBuf) -> WriteResult {
         self.inner.write_data(dest)
     }
+
+    fn data_length(&self) -> Option<usize> {
+        self.inner.data_length()
+    }
 }
 
 /// `Explicit` is a type which wraps another ASN.1 type, indicating that the tag is an ASN.1