Call through to inner size_hint

Currently our `size_hint` methods are calling `len` (from
`ExactSizeIterator`) which is incorrect. We should in fact call
`size_hint` on the inner iterator.

src/primitives/hrp.rs

@@ -207,7 +207,7 @@ pub struct ByteIter<'b> {
 impl<'b> Iterator for ByteIter<'b> {
     type Item = u8;
     fn next(&mut self) -> Option<u8> { self.iter.next().copied() }
-    fn size_hint(&self) -> (usize, Option<usize>) { (self.len(), Some(self.len())) }
+    fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
 }
 
 impl<'b> ExactSizeIterator for ByteIter<'b> {
@@ -230,7 +230,7 @@ pub struct CharIter<'b> {
 impl<'b> Iterator for CharIter<'b> {
     type Item = char;
     fn next(&mut self) -> Option<char> { self.iter.next().map(Into::into) }
-    fn size_hint(&self) -> (usize, Option<usize>) { (self.len(), Some(self.len())) }
+    fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
 }
 
 impl<'b> ExactSizeIterator for CharIter<'b> {
@@ -253,7 +253,7 @@ impl<'b> Iterator for LowercaseByteIter<'b> {
     fn next(&mut self) -> Option<u8> {
         self.iter.next().map(|b| if is_ascii_uppercase(b) { b | 32 } else { b })
     }
-    fn size_hint(&self) -> (usize, Option<usize>) { (self.len(), Some(self.len())) }
+    fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
 }
 
 impl<'b> ExactSizeIterator for LowercaseByteIter<'b> {
@@ -276,7 +276,7 @@ pub struct LowercaseCharIter<'b> {
 impl<'b> Iterator for LowercaseCharIter<'b> {
     type Item = char;
     fn next(&mut self) -> Option<char> { self.iter.next().map(Into::into) }
-    fn size_hint(&self) -> (usize, Option<usize>) { (self.len(), Some(self.len())) }
+    fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
 }
 
 impl<'b> ExactSizeIterator for LowercaseCharIter<'b> {