Fix clippy::needless_lifetimes lints

src/drawing_item.rs

@@ -19,7 +19,7 @@ pub enum DrawingItem<'a> {
     ViewPort(&'a ViewPort),
 }
 
-impl<'a> DrawingItem<'a> {
+impl DrawingItem<'_> {
     pub fn handle(&self) -> Handle {
         match self {
             DrawingItem::AppId(app_id) => app_id.handle,
@@ -53,7 +53,7 @@ pub enum DrawingItemMut<'a> {
     ViewPort(&'a mut ViewPort),
 }
 
-impl<'a> DrawingItemMut<'a> {
+impl DrawingItemMut<'_> {
     pub fn handle(&self) -> Handle {
         match self {
             DrawingItemMut::AppId(ref app_id) => app_id.handle,

src/entity_iter.rs

@@ -9,7 +9,7 @@ pub(crate) struct EntityIter<'a> {
     pub iter: &'a mut CodePairPutBack,
 }
 
-impl<'a> Iterator for EntityIter<'a> {
+impl Iterator for EntityIter<'_> {
     type Item = Entity;
 
     fn next(&mut self) -> Option<Entity> {
@@ -20,7 +20,7 @@ impl<'a> Iterator for EntityIter<'a> {
     }
 }
 
-impl<'a> EntityIter<'a> {
+impl EntityIter<'_> {
     pub(crate) fn read_entities_into_vec(&mut self, entities: &mut Vec<Entity>) -> DxfResult<()> {
         collect_entities(self, entities)
     }

src/object_iter.rs

@@ -5,7 +5,7 @@ pub(crate) struct ObjectIter<'a> {
     pub iter: &'a mut CodePairPutBack,
 }
 
-impl<'a> Iterator for ObjectIter<'a> {
+impl Iterator for ObjectIter<'_> {
     type Item = Object;
 
     fn next(&mut self) -> Option<Object> {