fix: pass unwrapped error to backoff/4 when compensate/4 returns bare :retry (#306)

When `compensate/4` returns bare `:retry`, `backoff/4` was receiving the
`RunStepError` wrapper instead of the inner error. This was inconsistent
with all other code paths, where `backoff/4` receives the unwrapped error.

Author: jimsynz

lib/reactor/executor/step_runner.ex

@@ -288,7 +288,7 @@ defmodule Reactor.Executor.StepRunner do
   defp handle_compensate_result(:retry, reactor, step, arguments, context, reason) do
     Hooks.event(reactor, :compensate_retry, step, context)
 
-    case Step.backoff(step, reason, arguments, context) do
+    case Step.backoff(step, reason.error, arguments, context) do
       delay when is_integer(delay) and delay > 0 -> {:backoff, delay, {:retry, reason}}
       _ -> {:retry, reason}
     end

test/reactor/executor/step_runner_test.exs

@@ -242,7 +242,7 @@ defmodule Reactor.Executor.StepRunnerTest do
       Example.Step.Compensable
       |> stub(:run, fn _, _, _ -> {:error, :doc} end)
       |> stub(:compensate, fn :doc, _, _, _ -> :retry end)
-      |> stub(:backoff, fn _, _, _, _ -> 100 end)
+      |> stub(:backoff, fn :doc, _, _, _ -> 100 end)
 
       assert {:backoff, 100, {:retry, %RunStepError{error: :doc}}} =
                run(reactor, state, step, nil)