Phase 2.5: Add turbulence backtest feature wrappers

bulk_richardson, theta_e_jump, and shear_at_top feature functions
pull derived fields from the nearest hrrr_native_profile. Ready for
mix backtest once sufficient data is backfilled.

lib/microwaveprop/backtest/features.ex

@@ -113,6 +113,52 @@ defmodule Microwaveprop.Backtest.Features do
     end
   end
 
+  @doc """
+  Bulk Richardson number at the inversion top from the nearest native profile.
+
+  Ri < 0.25 → turbulent (bad for propagation)
+  Ri > 1.0 → laminar (good for propagation)
+
+  Returns nil if no inversion detected or no native profile available.
+  """
+  @spec bulk_richardson(float, float, DateTime.t()) :: float | nil
+  def bulk_richardson(lat, lon, valid_time) do
+    with %HrrrNativeProfile{bulk_richardson: ri} when is_float(ri) <-
+           find_nearest_native(lat, lon, valid_time) do
+      ri
+    else
+      _ -> nil
+    end
+  end
+
+  @doc """
+  θₑ jump (K) across the inversion from the nearest native profile.
+
+  Larger positive values indicate stronger thermodynamic decoupling.
+  """
+  @spec theta_e_jump(float, float, DateTime.t()) :: float | nil
+  def theta_e_jump(lat, lon, valid_time) do
+    with %HrrrNativeProfile{theta_e_jump_k: jump} when is_float(jump) <-
+           find_nearest_native(lat, lon, valid_time) do
+      jump
+    else
+      _ -> nil
+    end
+  end
+
+  @doc """
+  Wind shear magnitude (m/s) at the inversion top from the nearest native profile.
+  """
+  @spec shear_at_top(float, float, DateTime.t()) :: float | nil
+  def shear_at_top(lat, lon, valid_time) do
+    with %HrrrNativeProfile{shear_at_top_ms: shear} when is_float(shear) <-
+           find_nearest_native(lat, lon, valid_time) do
+      shear
+    else
+      _ -> nil
+    end
+  end
+
   defp find_nearest_native(lat, lon, valid_time) do
     dlat = 0.07
     dlon = 0.07