Add EdgeCache encoding to BulkEdgeEncoder of codec-java

[zipdoki]

Summary

Extend BulkEdgeEncoder.bulkEncodeAll to also emit EdgeCache records during bulk load. Previously only HashEdge/IndexedEdge/CounterEdge rows were produced, so bulk-loaded data was missing from cache-backed (multi-hop) queries for INDEXED and MULTI_EDGE labels. Emitted rows are byte-compatible with what the V3 EdgeCacheRecordMapper writes — key layout xxhash32(src) | directedSource | labelId | EDGE_CACHE(-6) | direction | cacheCode(int32), qualifier cacheValues... | directedTarget, value ts | (propertyHashKey, propertyValue)..., and the IN-direction src/tgt swap in BytesKeyValueEdgeEncoder / StringKeyFieldValueEdgeEncoder mirrors V3 EdgeMutationStrategy.MultiEdge. Fixes the behavior gap noted in #37.

Test plan

• ./gradlew :codec-java:build — full codec-java compile; catches type/import breakage from the new Cache DTO, LabelDTO.caches field, EncodedEdgeType.EDGE_CACHE_TYPE(-6), and the EdgeEncoder.encodeCacheEdge / encodeAllCacheEdges additions.
• ./gradlew :codec-java:test --tests "*BulkEdgeEncoderTests*" — INDEXED label encoding across BOTH / OUT / IN directions with total row-count assertions, HASH / inactive-edge negative cases (no cache rows even when caches is set), and the backward-compat path where a label JSON without a caches key still deserializes and emits no cache rows.
• ./gradlew :codec-java:test --tests "*MultiEdgeBulkEdgeEncoderTests*" — MULTI_EDGE label; verifies the synthetic outEdge=(src, id) / inEdge=(id, tgt) from the bulk path are reused by the cache encoder and emit 2 cache rows (OUT/IN). Also covers MULTI_EDGE JSON without caches.
• ./gradlew :core:test --tests "*V2MultiEdgeBulkLoadTest*" — end-to-end round-trip: V2 bytes produced by BulkEdgeEncoder are decoded via V3 EdgeCacheRecordMapper.Decoder (testEdgeCacheOut/In), proving byte compatibility with V3's wire format. Also regresses state/indexed/counter paths to ensure the cache-row addition did not disturb them.
• Manual multi-hop cache-backed query after bulk load — confirms bulk-loaded edges surface in cache-path multi-hop queries.
• Grep audit for getCaches() / entity.caches under codec-java/ and engine/ — confirms no production caller expects a non-null LabelDTO.caches after the null-guard removal (BulkEdgeEncoder is the only Java consumer and already does caches != null && !caches.isEmpty(); Kotlin LabelEntity.caches is a separate class with a Kotlin emptyList() default and is unaffected).

[em3s]

Note - Although the migration to V3 is in progress, this PR is a necessary update to V2 to bring the latest features into the currently running production.

@zipdoki
BTW, was this tested against HBase? Mutation and simple query are being implemented, so you can test against those.

[em3s]

@zipdoki

Need to check whether the LabelDTO change impacts any of its usages.

If the above and HBase testing are confirmed, I'll go ahead with an optimistic merge.

[zipdoki]

@em3s
Will test these two and report back:

• HBase (mutation + simple query)
• LabelDTO usage impact