Add v2 RetrievalGen benchmark (test/validation, no-profile, top5 same-market retrieval)

v2/benchmark_retrievalgen/benchmark_metadata.json

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+{
+  "version": "retrievalgen_v2_top5_market_noprofile",
+  "description": "RetrievalGen benchmark without wallet profile. CurrentMarketHistory + RetrievedMarketTraces (Top5 same-market neighbors).",
+  "rows": {
+    "test": 59559,
+    "validation": 114471
+  },
+  "retrieval": {
+    "scope": "same market",
+    "top_k": 5,
+    "neighbor_trades": "all trades before current sample time",
+    "causality": "strictly before current sample time (block, log_index)",
+    "similarity": "0.4 act + 0.2 outcome + 0.2 price + 0.15 size + 0.05 tempo"
+  },
+  "support_set": "v2/support_set"
+}

v2/benchmark_retrievalgen/test.jsonl.gz

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+version https://git-lfs.github.com/spec/v1
+oid sha256:3ed8489b0e94138a9187e54bb9a0dc26d7171851edfeb20f61793551562bba93
+size 29645534

v2/benchmark_retrievalgen/validation.jsonl.gz

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:41a20885a102eecc826bdd8977b1ba69e3fc36a62a40055c45df508a1746934f
+size 54452878