fix(batch): handle happy path

BatchContext can deal with happy path, i.e. no oom, no shutdowns, etc.

Author: bevzzz

src/main/java/io/weaviate/client6/v1/api/collections/batch/Batch.java

@@ -267,6 +267,7 @@ synchronized Collection<String> clear() {
 
       Set<String> removed = Set.copyOf(buffer.keySet());
       buffer.clear();
+      sizeBytes = 0;
 
       if (pendingMaxSize.isPresent()) {
         setMaxSize(pendingMaxSize.getAsInt());