fix(print): keep derived physical_extruder_map in the original-config snapshot

Print::apply() derives physical_extruder_map from printer_extruder_id and writes
it into new_full_config, but does so after m_ori_full_print_config is snapshotted.
The selector write-back path rebuilds m_full_print_config from that snapshot, so
m_full_print_config kept the unexpanded default while every subsequent apply
re-derived the expanded map. An unchanged config therefore diffed on
physical_extruder_map on every re-apply, and since that key is not handled by
invalidate_state_by_config_options() it fell through to the catch-all and
invalidated every step — forcing a full reslice on each apply.

Mirror the derived map into the snapshot so the two stay consistent.

Caught by the upstream test 'Selector write-back expands migrating filaments and
survives re-apply', which asserts a re-applied unchanged config is not
APPLY_STATUS_INVALIDATED.

src/libslic3r/PrintApply.cpp

@@ -1237,8 +1237,16 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
     {
         auto* pem = new_full_config.option<ConfigOptionInts>("physical_extruder_map", true);
         const auto* pei = new_full_config.option<ConfigOptionInts>("printer_extruder_id");
-        if (pem)
+        if (pem) {
             pem->values = effective_physical_extruder_map(pem, pei).values;
+            // m_ori_full_print_config was snapshotted above, before this derivation, and the
+            // selector write-back path rebuilds m_full_print_config from that snapshot. Without
+            // mirroring the derived map into it, m_full_print_config keeps the unexpanded default
+            // while every later apply re-derives the expanded one, so an unchanged config diffs
+            // on physical_extruder_map forever and invalidates all steps on every re-apply.
+            if (auto* ori_pem = m_ori_full_print_config.option<ConfigOptionInts>("physical_extruder_map", true))
+                ori_pem->values = pem->values;
+        }
     }
 
     auto opt_filament_map = new_full_config.option<ConfigOptionInts>("filament_map");