Improve data pipeline

pipeline/transform/price_estimation/backtest.py

@@ -67,6 +67,16 @@ def extract_test_set(input_path: Path) -> pl.DataFrame:
             .struct.field("price")
             .alias("input_price"),
         )
+        .with_columns(
+            # Date of the input (second-to-last) sale, used by the kNN leakage
+            # filter to exclude the target property's own prior sale from its
+            # comparables. Built from year+month (day defaults to the 1st).
+            pl.date(
+                pl.col("input_year").cast(pl.Int32),
+                pl.col("input_month").cast(pl.Int32),
+                1,
+            ).alias("input_date"),
+        )
         .with_columns(
             (
                 pl.col("actual_year").cast(pl.Float64)