further optimize uptime retrival

Try and minimize expensive operations (e.g., divisions and allocations) to hopefully get a
*consistent* measurable performance improvement. In my testing this brings the get_current
function duration from > 1.2600 µs to < 1.2400 µs.

src/uptime.rs

@@ -5,16 +5,29 @@ pub fn get_current() -> Result<String, io::Error> {
     let info = sysinfo().map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
     let uptime_seconds = info.uptime().as_secs();
 
-    let total_minutes = uptime_seconds / 60;
-    let days = total_minutes / (60 * 24);
-    let hours = (total_minutes % (60 * 24)) / 60;
-    let minutes = total_minutes % 60;
+    let days = uptime_seconds / (60 * 60 * 24);
+    let hours = (uptime_seconds / 3600) % 24;
+    let minutes = (uptime_seconds / 60) % 60;
 
-    let parts = [(days, "day"), (hours, "hour"), (minutes, "minute")]
-        .iter()
-        .filter(|&&(value, _)| value > 0)
-        .map(|&(value, label)| format!("{value} {label}{}", if value > 1 { "s" } else { "" }))
-        .collect::<Vec<_>>();
+    let mut result = String::new();
+    if days > 0 {
+        result.push_str(&format!("{days} day{}", if days > 1 { "s" } else { "" }));
+    }
+    if hours > 0 {
+        if !result.is_empty() {
+            result.push_str(", ");
+        }
+        result.push_str(&format!("{hours} hour{}", if hours > 1 { "s" } else { "" }));
+    }
+    if minutes > 0 {
+        if !result.is_empty() {
+            result.push_str(", ");
+        }
+        result.push_str(&format!(
+            "{minutes} minute{}",
+            if minutes > 1 { "s" } else { "" }
+        ));
+    }
 
-    Ok(parts.join(", "))
+    Ok(result)
 }