[improve][ml] Improve cache insert performance by removing exists check since it's already covered by putIfAbsent (#24699)

(cherry picked from commit 669ab61)

Author: lhotari

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/cache/RangeEntryCacheImpl.java

@@ -139,12 +139,6 @@ public boolean insert(Entry entry) {
                     entryLength);
         }
 
-        Position position = entry.getPosition();
-        if (entries.exists(position)) {
-            // If the entry is already in the cache, don't insert it again
-            return false;
-        }
-
         ByteBuf cachedData;
         if (copyEntries) {
             cachedData = copyEntry(entry);
@@ -156,6 +150,7 @@ public boolean insert(Entry entry) {
             cachedData = entry.getDataBuffer().retain();
         }
 
+        Position position = entry.getPosition();
         ReferenceCountedEntry cacheEntry =
                 EntryImpl.createWithRetainedDuplicate(position, cachedData, entry.getReadCountHandler());
         cachedData.release();