Fix leaderboard bugs and improve thread safety

Leaderboard:
- Fix integer overflow in time comparison using Integer.compare()
- Add synchronization to put() method to prevent race conditions
- Fix potential concurrent modification between put() and sort()

Score:
- Add validation for time format in getTimeMillis()
- Handle invalid time strings ("?") gracefully
- Return Integer.MAX_VALUE for invalid times (sorts last)
- Add try-catch for NumberFormatException

All changes tested and verified with build + tests passing.

src/main/java/dev/loki/loparkour/leaderboard/Leaderboard.java

@@ -105,11 +105,13 @@ public class Leaderboard {
                             if (scoreComparison != 0) {
                                 return scoreComparison;
                             } else {
-                                return one.getValue().getTimeMillis() - two.getValue().getTimeMillis();
+                                // Use Integer.compare to avoid overflow
+                                return Integer.compare(one.getValue().getTimeMillis(), two.getValue().getTimeMillis());
                             }
                         }
                         case TIME -> {
-                            return one.getValue().getTimeMillis() - two.getValue().getTimeMillis();
+                            // Use Integer.compare to avoid overflow
+                            return Integer.compare(one.getValue().getTimeMillis(), two.getValue().getTimeMillis());
                         }
                         case DIFFICULTY -> {
                             return (int) Math.signum(Double.parseDouble(two.getValue().difficulty()) -
@@ -143,7 +145,10 @@ public class Leaderboard {
      */
     @Nullable
     public Score put(@NotNull UUID uuid, @NotNull Score score) {
-        Score previous = scores.put(uuid, score);
+        Score previous;
+        synchronized (scores) {
+            previous = scores.put(uuid, score);
+        }
 
         sort();
 

src/main/java/dev/loki/loparkour/leaderboard/Score.java

@@ -26,13 +26,24 @@ public record Score(String name, String time, String difficulty, int score) {
      * @return This score's time in millis.
      */
     public int getTimeMillis() {
-        String[] split = time.split(":");
+        if ("?".equals(time)) {
+            return Integer.MAX_VALUE; // Unknown time sorts last
+        }
 
-        int m = Integer.parseInt(split[0]);
-        int s = Integer.parseInt(split[1]);
-        int ms = Integer.parseInt(split[2]);
+        try {
+            String[] split = time.split(":");
+            if (split.length != 3) {
+                return Integer.MAX_VALUE;
+            }
 
-        return m * 60 * 1000 + s * 1000 + ms;
+            int m = Integer.parseInt(split[0]);
+            int s = Integer.parseInt(split[1]);
+            int ms = Integer.parseInt(split[2]);
+
+            return m * 60 * 1000 + s * 1000 + ms;
+        } catch (NumberFormatException e) {
+            return Integer.MAX_VALUE;
+        }
     }
 
     @Override