Fix VariablePredicate skipping getValue() when no value predicate is set

[Copilot]

VariablePredicate.test() was calling variable.getValue() even when valuePredicate was absent, causing EvaluationException for operator variables with empty inputs (e.g. new int[0] in tests). Since ValuePredicate.ANY always returns true, the evaluation was purely wasteful — and fatal for structurally-valid-but-unevaluable LazyExpression instances.

Change

VariablePredicate.test() — skip getValue() when no value predicate is specified:

// Before
&& valuePredicate.orElse(ValuePredicate.ANY).test(variable.getValue())

// After
&& (this.valuePredicate.isEmpty() || this.valuePredicate.get().test(variable.getValue()))

This means getValue() is only called when there is an explicit value to compare against. Operator-type advancement predicates (which only check operator identity and input structure, not the evaluated output) now work correctly even when the variable cannot be evaluated due to missing network inputs.

Unblocks integrateddynamics:part_writer_aspect criterion checks in IntegratedTunnels for advancements like export_items_limit, filter_storage_mod, and place_logwood.

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[coveralls]

coverage: 45.571% (-0.1%) from 45.677%
when pulling 13c04ff on copilot/fix-advancement-game-tests
into b464674 on master-1.21-lts.