refactor: centralize BYTES_PER_MB and tidy peer IP parsing

- Add pub const BYTES_PER_MB to ui/utils.rs and replace 7 uses of the
  bare 1_048_576.0 literal across the UI modules. Also pick up
  uninlined-format-args cleanup in the same file while we're here.
- Replace Vec<i32> IP-byte accumulator in Peer::new_from_message with a
  [u8; 4]; the .abs() calls on u8.into() were no-ops on always-positive
  values. Network byte order ([3].[2].[1].[0]) preserved; tests cover
  the wire format.

soulseek-rs-lib/src/peer/mod.rs

@@ -119,17 +119,13 @@ impl Peer {
         let username = message.read_string();
         let connection_type = message.read_string().parse().unwrap();
 
-        let mut ip: Vec<i32> = vec![];
-        for _ in 0..4 {
-            ip.push(message.read_int8().into());
-        }
-        let host: String = format!(
-            "{}.{}.{}.{}",
-            ip[3].abs(),
-            ip[2].abs(),
-            ip[1].abs(),
-            ip[0].abs()
-        );
+        let ip = [
+            message.read_int8(),
+            message.read_int8(),
+            message.read_int8(),
+            message.read_int8(),
+        ];
+        let host = format!("{}.{}.{}.{}", ip[3], ip[2], ip[1], ip[0]);
 
         let (port, token, privileged, unknown, obfuscated_port) = (
             message.read_int32(),