removed some deps, using heap to store the current ringer (makes it more dynamic)

src/ringer.rs

@@ -1,11 +1,12 @@
 use std::{
+    fmt::Debug,
     sync::{Arc, Mutex},
     thread,
 };
 
 use gpio_cdev::{Chip, LineRequestFlags};
 
-pub trait Ringer: Send + Sync {
+pub trait Ringer: Send + Sync + Debug {
     fn ring(&self) -> Result<(), String>;
 }
 
@@ -71,6 +72,7 @@ impl Ringer for BeepRinger {
 
 /// Used for local testing without an actual beeper or similar. The only thing it does is print
 /// that it's ringing.
+#[derive(Debug)]
 pub struct SilentRinger;
 
 impl SilentRinger {