feat(v3/sem): pin ORE comparators IMMUTABLE + regression test

[tobyhede]

What

Mark the three eql_v3.compare_ore_block_u64_8_256_term(s) overloads IMMUTABLE (term×term, term[]×term[], composite×composite). They previously had no volatility marker and defaulted to VOLATILE.

Why

The comparison is deterministic — its only crypto call, pgcrypto encrypt(), is itself IMMUTABLE STRICT PARALLEL SAFE — so marking the comparators IMMUTABLE lets the planner fold/cache them in ordering and index contexts.

 CREATE FUNCTION eql_v3.compare_ore_block_u64_8_256_term(a …, b …)
   RETURNS integer
+  IMMUTABLE
   SET search_path = pg_catalog, extensions, public

NOT STRICT: the NULL-handling branches in the array overload are load-bearing — a STRICT marker would let PostgreSQL skip the body on a NULL argument.

Test

family::sem::ore_comparators_are_immutable (T8) asserts exactly 3 overloads exist and all carry provolatile = 'i', so a silent regression to VOLATILE fails CI.

Summary by CodeRabbit

Release Notes

• Improvements

  • Encrypted data comparison functions now explicitly declared as immutable for enhanced query optimization and performance.
  • Enhanced documentation clarifying deterministic comparison behavior and NULL-handling expectations.

• Tests

  • Added test coverage to validate immutability declarations and prevent future regressions.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch v3-sem-ore-immutable

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