src: address a bunch of clippy::pedantic lints

src/span.rs

@@ -16,7 +16,7 @@ impl std::fmt::Debug for Span {
 
 #[expect(non_snake_case)]
 /// Stores the start and end byte position
-pub fn Span(head: u32, tail: u32) -> Span {
+pub const fn Span(head: u32, tail: u32) -> Span {
     Span { head, tail }
 }