CASSJAVA-68 Improve DefaultCodecRegisry.CacheKey#hashCode() to eliminate Object[] allocation (found via profiler)

patch by Tatu Saloranta; reviewed by Dmitry Konstantinov and Bret McGuire for CASSJAVA-68

Author: tatu-at-datastax

core/src/main/java/com/datastax/oss/driver/internal/core/type/codec/registry/DefaultCodecRegistry.java

@@ -159,7 +159,10 @@ public boolean equals(Object other) {
 
     @Override
     public int hashCode() {
-      return Objects.hash(cqlType, javaType, isJavaCovariant);
+      // NOTE: inlined Objects.hash for performance reasons (avoid Object[] allocation
+      // seen in profiler allocation traces)
+      return ((31 + Objects.hashCode(cqlType)) * 31 + Objects.hashCode(javaType)) * 31
+              + Boolean.hashCode(isJavaCovariant);
     }
   }
 }