Add a non-incremental / batch oracle to the indexed left-join property tests - #6855

…tests. The oracle integrates both inputs, computes matched rows with stream_join, derives right-key presence with stream_aggregate, and subtracts unmatched candidates whose keys occur on the right. It supports signed Z-set weights, including keys represented only by negative weights.

The existing reference implementation remains in place and checks left join through a composition of incremental operators. The new oracle recomputes from accumulated batches, independently covering the incrementalization behavior used by both ordinary and balanced left joins in per-step and transaction modes.

The indexed left-join property tests drew weights from
generate_join_test_data(10, 5, 1, 50). Weights come from the half-open
range -max_weight..max_weight, so max_weight = 1 yielded only {-1, 0}.
Zero-weight tuples are no-ops, which made every non-trivial tuple a
deletion: the non-incremental batch oracle never saw an insert, and
multiplicity above 1 never arose. Raise max_weight to 3, matching every
other call site in the crate, so the tests cover insertions, deletions,
multiplicity, and mixed cancellation.

Also document the oracle's matched + unmatched - suppressed algebra, and
in particular why the unit weight of right_presence makes the
cancellation exact for signed weights. Replace plus(&suppressed.neg())
with minus(&suppressed), name the third closure clone suppressed_f for
symmetry with matched_f and unmatched_f, and give the assertions messages
that identify which oracle disagreed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>