Add more Debug implementations

I generally like to implement Debug on these kind of types.

src/font/mod.rs

@@ -14,6 +14,7 @@ pub use font_inner::Font;
 mod font_inner {
     use super::*;
     use aliasable::boxed::AliasableBox;
+    use core::fmt;
 
     /// A font
     //
@@ -31,6 +32,14 @@ mod font_inner {
         id: fontdb::ID,
     }
 
+    impl fmt::Debug for Font {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.debug_struct("Font")
+                .field("id", &self.id)
+                .finish_non_exhaustive()
+        }
+    }
+
     pub(super) struct FontTryBuilder<
         RustybuzzBuilder: for<'this> FnOnce(
             &'this Arc<dyn AsRef<[u8]> + Send + Sync>,

src/font/system/mod.rs

@@ -15,6 +15,7 @@ pub use fontdb;
 pub use rustybuzz;
 
 /// A value borrowed together with an [`FontSystem`]
+#[derive(Debug)]
 pub struct BorrowedWithFontSystem<'a, T> {
     pub(crate) inner: &'a mut T,
     pub(crate) font_system: &'a mut FontSystem,

src/font/system/no_std.rs

@@ -9,6 +9,7 @@ use alloc::{
 use crate::{Attrs, Font};
 
 /// Access system fonts
+#[derive(Debug)]
 pub struct FontSystem {
     locale: String,
     db: fontdb::Database,

src/font/system/std.rs

@@ -5,6 +5,7 @@ use std::{collections::HashMap, sync::Arc};
 use crate::{Attrs, AttrsOwned, Font};
 
 /// Access system fonts
+#[derive(Debug)]
 pub struct FontSystem {
     locale: String,
     db: fontdb::Database,