Add pancancer metadata

pancancer_metadata.json

@@ -0,0 +1,18 @@
+{
+  "dataset_name": "pancancer",
+  "download_urls": {
+    "proteomics": "https://ars.els-cdn.com/content/image/1-s2.0-S1535610822002744-mmc3.xlsx",
+    "drug_response": "https://figshare.com/ndownloader/files/34355645"
+  },
+  "download_timestamp": "2025-07-29 11:49:43.234780",
+  "statistics": {
+    "num_samples": 2725,
+    "num_features": 8504,
+    "target_stats": {
+      "mean": 4.3934604524007925,
+      "std": 1.064020465622011,
+      "min": -1.0390868718714783,
+      "max": 8.664123054729536
+    }
+  }
+}