Fix NumPy typecheck errors.

Author: edtechre

src/pybroker/eval.py

@@ -453,9 +453,9 @@ def iqr(values: NDArray[np.float64]) -> float:
     x = values[~np.isnan(values)]
     if not len(x):
         return 0
-    q75: float
-    q25: float
-    q75, q25 = tuple(np.percentile(x, [75, 25], method="midpoint"))
+    percentiles = tuple(np.percentile(x, [75, 25], method="midpoint"))
+    q75: float = float(percentiles[0])
+    q25: float = float(percentiles[1])
     return q75 - q25