Backport storage-ops shadow testing to 0.2.x

[em3s]

Summary

Backports the storage-ops shadow-testing feature to the v0.2.x line for the v0.2.1 release. Cherry-picks four squash-merged main commits in order: #258 -> #259 -> #261 -> #254.

With the AB-Include-Mutation-Context: true header, mutation responses surface the HBase Put / Delete / Increment ops actually issued to storage under context["storageOps"], base64-encoded. Without the header the wire format is unchanged.

Cherry-picked commits

Upstream	SHA	Contents
#258	3692c41	context: Map<String, Any>? on V2 / V3 mutation response items
#259	1ef1b6d	AB-Include-Mutation-Context header + e2e non-breaking verification
#261	5e97d9b	StorageOpCollector scaffold + mutation-path wiring
#254	9bfa878	collect() implementation for Put / Delete / Increment + tests

Conflict resolution

All conflicts landed in #261 and were limited to the import region — 0.2.x does not have main's post-v0.2.0 refactors (engine.sql.DataFrame, engine.query.LabelProvider, etc.). Resolved by keeping the 0.2.x imports as-is and adding only the StorageOpCollector import. No behavioral changes beyond what the four upstream commits define.

Affected files:

• engine/binding/TableBinding.kt
• v2/engine/Graph.kt
• v2/engine/v3/NilTableBinding.kt
• v2/engine/v3/V2BackedTableBinding.kt

Test plan

./gradlew build locally passed. Key suites:

• StorageOpCollectorTest — round-trip per op type, multi-CF Put, multi-byte value, truncation, Append → Unknown, non-Mutation fallthrough
• CdcContextSerializationTest — storageOps / storageOpsTruncated excluded from CDC JSON
• V2EdgeStorageOpsSpec — V2 /graph/v2/edge with / without header
• EdgeMutationStorageOpsSpec — V3 edge + multi-edge with header
• MutationResultItemContextTest, MutationContextOptInE2ETest — context field shape and opt-in gating