nws: refactored the NWS source files to relocate normalization logic to internal/normalizers.

internal/normalizers/common/units.go

@@ -0,0 +1,15 @@
+// FILE: ./internal/normalizers/common/units.go
+package common
+
+// Common unit conversions used across providers.
+//
+// These helpers are intentionally small and “obvious” and are meant to remove
+// duplication across normalizers (and eventually across sources, once refactored).
+
+func TempCFromF(f float64) float64 { return (f - 32.0) * 5.0 / 9.0 }
+func TempCFromK(k float64) float64 { return k - 273.15 }
+
+func SpeedKmhFromMps(ms float64) float64  { return ms * 3.6 }
+func SpeedKmhFromMph(mph float64) float64 { return mph * 1.609344 }
+
+func PressurePaFromHPa(hpa float64) float64 { return hpa * 100.0 }