refactor: centralize numeric normalization

app/backend/data/numbers.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+import math
+from typing import Any
+
+
+def finite_number(value: Any, default: float = 0.0) -> float:
+    try:
+        number = float(value)
+        return number if math.isfinite(number) else default
+    except (TypeError, ValueError):
+        return default
+
+
+def non_nan_number(value: Any, default: float = 0.0) -> float:
+    try:
+        number = float(value)
+        return number if number == number else default
+    except (TypeError, ValueError):
+        return default