chore: improve code quality

Removed a lot of magic constants. Gave them descriptive variable names

src/high_ram.rs

@@ -1,22 +1,25 @@
+const HIGH_RAM_SIZE: usize = 127;
+const HIGH_RAM_START_ADDRESS: usize = 0xFF80;
+
 #[derive(Debug, Clone)]
 pub struct HighRam {
-    buf: Box<[u8; 127]>,
+    buf: Box<[u8; HIGH_RAM_SIZE]>,
 }
 
 impl Default for HighRam {
     fn default() -> Self {
         Self {
-            buf: Box::new([0u8; 127]),
+            buf: Box::new([0u8; HIGH_RAM_SIZE]),
         }
     }
 }
 
 impl HighRam {
     pub fn write_byte(&mut self, addr: u16, byte: u8) {
-        self.buf[addr as usize - 0xFF80] = byte;
+        self.buf[addr as usize - HIGH_RAM_START_ADDRESS] = byte;
     }
 
     pub fn read_byte(&self, addr: u16) -> u8 {
-        self.buf[addr as usize - 0xFF80]
+        self.buf[addr as usize - HIGH_RAM_START_ADDRESS]
     }
 }