refactor: stop returning impl in print feature

packages/mrml-core/src/mj_attributes_element/print.rs

@@ -1,13 +1,20 @@
-use crate::prelude::print::{PrintableAttributes, PrintableElement};
+use crate::prelude::{hash::Map, print::PrintableElement};
 
 impl PrintableElement for super::MjAttributesElement {
+    type Attrs = Map<String, String>;
+    type Children = ();
+
     fn tag(&self) -> &str {
         self.name.as_str()
     }
 
-    fn attributes(&self) -> &impl PrintableAttributes {
+    fn attributes(&self) -> &Self::Attrs {
         &self.attributes
     }
+
+    fn children(&self) -> &Self::Children {
+        &()
+    }
 }
 
 #[cfg(test)]

packages/mrml-core/src/mj_include/body/print.rs

@@ -11,13 +11,20 @@ impl PrintableAttributes for super::MjIncludeBodyAttributes {
 }
 
 impl PrintableElement for super::MjIncludeBody {
+    type Attrs = super::MjIncludeBodyAttributes;
+    type Children = ();
+
     fn tag(&self) -> &str {
         super::NAME
     }
 
-    fn attributes(&self) -> &impl PrintableAttributes {
+    fn attributes(&self) -> &Self::Attrs {
         &self.0.attributes
     }
+
+    fn children(&self) -> &Self::Children {
+        &()
+    }
 }
 
 #[cfg(test)]

packages/mrml-core/src/mj_include/head/print.rs

@@ -2,13 +2,20 @@ use super::MjIncludeHeadKind;
 use crate::prelude::print::{PrintableAttributes, PrintableElement};
 
 impl PrintableElement for super::MjIncludeHead {
+    type Attrs = super::MjIncludeHeadAttributes;
+    type Children = ();
+
     fn tag(&self) -> &str {
         super::NAME
     }
 
-    fn attributes(&self) -> &impl PrintableAttributes {
+    fn attributes(&self) -> &Self::Attrs {
         &self.0.attributes
     }
+
+    fn children(&self) -> &Self::Children {
+        &()
+    }
 }
 
 impl PrintableAttributes for super::MjIncludeHeadAttributes {

packages/mrml-core/src/prelude/print.rs

@@ -53,15 +53,18 @@ impl<C: Printable> PrintableChildren for Vec<C> {
 impl<T: StaticTag, A: PrintableAttributes, C: PrintableChildren> PrintableElement
     for super::Component<PhantomData<T>, A, C>
 {
+    type Attrs = A;
+    type Children = C;
+
     fn tag(&self) -> &str {
         T::static_tag()
     }
 
-    fn attributes(&self) -> &impl PrintableAttributes {
+    fn attributes(&self) -> &Self::Attrs {
         &self.attributes
     }
 
-    fn children(&self) -> &impl PrintableChildren {
+    fn children(&self) -> &Self::Children {
         &self.children
     }
 }
@@ -131,13 +134,12 @@ pub trait Printable {
 }
 
 pub trait PrintableElement {
+    type Attrs: PrintableAttributes;
+    type Children: PrintableChildren;
+
     fn tag(&self) -> &str;
-    fn attributes(&self) -> &impl PrintableAttributes {
-        &()
-    }
-    fn children(&self) -> &impl PrintableChildren {
-        &()
-    }
+    fn attributes(&self) -> &Self::Attrs;
+    fn children(&self) -> &Self::Children;
 }
 
 impl<E: PrintableElement> Printable for E {