Skip Hibernate deep copy for ValueEntity.data JSON column

[stalep]

Summary

• Add @Mutability(Immutability.class) to ValueEntity.data so Hibernate uses reference equality for dirty-checking instead of deserializing and comparing the full JSON tree

Problem

Hibernate's FormatMapperBasedJavaType.deepCopy deserializes and re-serializes the JSONB data column on every flush to create a snapshot for dirty comparison. Profiling showed this consumed ~50% of CPU during uploads (deepCopy + dirty-checking combined).

Fix

@Mutability(Immutability.class) tells Hibernate the field value is never mutated in-place — changes are only made by replacing the reference (data = newData). Hibernate then uses the original reference as the snapshot and compares with == instead of deep tree comparison.

All code paths that modify data use reference replacement, never in-place mutation (e.g., no data.put("key", val)), so reference equality is correct.

Benchmark — rhivos-perf-comprehensive legacy import (5 runs, 4 workers, PostgreSQL)

Metric	Before	After	Change
Wall-clock	1m36s	1m20s	-17%
CPU user	2m02s	0m59s	-51%
dirty-checking samples	3,946	2	-99.97%
deepCopy samples	2,169	0	-100%
GC samples	1,764	1,572	-11%

Test plan

• All 207 existing tests pass
• Verified no code path mutates data in-place — all are reference replacements
• Recalculation tests confirm dirty detection still works for existingValue.data = newValue.data reassignment