Skip Hibernate deep copy for ValueEntity.data JSON column

Add @mutability(Immutability.class) to the JSONB data field so Hibernate
uses reference equality instead of deserialize-compare-reserialize for
dirty checking. All code paths that modify data use reference replacement
(data = newData), never in-place mutation, so reference equality is
correct.

Profiling showed deepCopy + dirty-checking of the JSON column consumed
~50% of CPU during uploads. This eliminates both entirely — deepCopy
drops to 0 samples, dirty-checking to near-zero. Wall-clock improvement
of ~17% on a 4-worker rhivos import (1m36s to 1m20s) with CPU user time
cut in half (2m02s to 59s).

Author: stalep

src/main/java/io/hyperfoil/tools/h5m/entity/ValueEntity.java

@@ -9,7 +9,9 @@
 import jakarta.persistence.*;
 import org.hibernate.annotations.CreationTimestamp;
 import org.hibernate.annotations.JdbcTypeCode;
+import org.hibernate.annotations.Mutability;
 import org.hibernate.type.SqlTypes;
+import org.hibernate.type.descriptor.java.Immutability;
 
 import java.time.LocalDateTime;
 import java.util.*;
@@ -25,6 +27,7 @@ public class ValueEntity extends PanacheEntity {
     @Column(columnDefinition = "JSONB")
     @JdbcTypeCode(SqlTypes.JSON)
     @Basic(fetch = FetchType.LAZY)
+    @Mutability(Immutability.class)
     public JsonNode data;
 
     //not yet used but the idea is to sort multiple values based on idx to preserve node output order for next nodes input