feat(writer): cascade delta like Rust's DeltaScheme, edition-gated (issue #410)

[dfa1]

Fixes #440.
Closes #410: Rust-parity port 4/4, after RunEnd (#435), ZigZag (#436) and RLE (#437, plus float RLE in #438).

Delta

• DeltaEncodingEncoder.encodeCascade: bases and deltas (Rust ids 0/1, also our wire order) become open children, with Rust's DeltaScheme exclusion (Delta on both, so data is never delta-encoded twice).
• Arrays shorter than one FastLanes chunk are skipped (Rust's MIN_DELTA_LEN = 1024).
• Edition-gated like Rust: Rust registers DeltaScheme, but notes "no edition includes fastlanes.delta yet, so the session's enabled editions decide". It is offered as a cascade candidate only when an enabled edition contains it (unstable2025.05.0+, the same gate as OnPair). Default writes never emit it.
• Rust's ancestor rule (no Delta on Dict codes) is moot: Delta joins the cascade only via an unstable edition, and Dict's CODES_EXCLUDED already bars Sequence there. Noted for a follow-up if we want it literal.
• The shared delta computation moves into one Deltas helper used by encode and encodeCascade; the terminal output is unchanged.
• Rust's ratio-callback estimate (1.25× bar, 0.95 penalty) is not ported. Our cascade measures by sampling, so this is a selection-heuristic difference, not a format one.

Bug fix found on the way (edition guard)

editionExcluded only covered the encoders the writer itself lists. SparseEncodingEncoder keeps a private candidate list for compressing a validity bitmap's patch indices, and it offers fastlanes.delta. Plain delta always lost there, so this never surfaced. Once delta cascades it wins, and a default-edition write then failed the backstop guard (fastlanes.delta: outside the configured edition(s) [core2026.08.0]). This reproduced in 3 FileSizeComparison tests. editionExcluded now covers every well-known id outside the enabled editions. That is safe by construction: anything it removes would have failed the backstop anyway.

Tests

• WriterEditionGuardTest: with default editions, cascading never emits delta; the unstable edition picks it on jittered timestamps and reads back exactly; and the private-candidate-list regression (fails without the fix, verified with a clean build).
• DeltaEncodingEncoderTest.Cascade: children equal the terminal buffers, exclusions, and the under-one-chunk skip.
• Interop javaWriter_jniReader_delta_cascading_unstableEdition: vortex-jni reads the cascaded delta file on a full scan, a mid-chunk row range and a zone-pruned filter.
• Default-edition sizes are byte-identical. Green: writer suite plus 370 integration tests.

Docs: docs/compatibility.md delta row, plus the CHANGELOG.

🤖 Generated with Claude Code