seed: call pre and post at the correct place

Call pre- and postprocessing at the correct place in SeedMixin,
so only before and after the actaul optimization.

src/rtctools/optimization/seed_mixin.py

@@ -109,10 +109,18 @@ def optimize(
         postprocessing: bool = True,
         log_solver_failure_as_error: bool = True,
     ) -> bool:
+        if preprocessing:
+            self.pre()
         self._seed_timeseries = self.seed_options().seed_timeseries
         fallback = self.seed_options().fallback
-        success = super().optimize(preprocessing, postprocessing, log_solver_failure_as_error)
+        success = super().optimize(
+            preprocessing=False,
+            postprocessing=False,
+            log_solver_failure_as_error=log_solver_failure_as_error,
+        )
         if not success and self._use_seed_timeseries() and fallback:
             self._seed_timeseries = None
             success = super().optimize(preprocessing, postprocessing, log_solver_failure_as_error)
+        if postprocessing:
+            self.post()
         return success