BREAKING CHANGE: improvement(lib): use u64 for Printer::display_offset and Squeezer::process, not usize

Technically a breaking change for architectures where
`size_of::<usize>() > size_of::<u64>()`, but that strikes me as
extremely unlikely.

This change is important because most file seek offsets, even on older
architectures with word sizes smaller than `u32`, accept a `u64`. In
particular, Rust's own `std` acknowledges this. So, we're actually going
against prior art in Rust by using a `usize`.

src/bin/hexyl.rs

@@ -149,7 +149,7 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
     let mut stdout_lock = stdout.lock();
 
     let mut printer = Printer::new(&mut stdout_lock, show_color, border_style, squeeze);
-    printer.display_offset(display_offset as usize);
+    printer.display_offset(display_offset);
     printer.print_all(&mut reader)?;
 
     Ok(())