Fix layer time slowdown

The recent GCode writer changes which put the speed changes on a line of
their own have caused the layer time slowdown to be ignored by the regex
in CoolingBuffer.pm.

Fixes: #3134

lib/Slic3r/GCode/CoolingBuffer.pm

@@ -56,7 +56,7 @@ sub flush {
         Slic3r::debugf "  fan = %d%%, speed = %d%%\n", $fan_speed, $speed_factor * 100;
 
         if ($speed_factor < 1) {
-            $gcode =~ s/^(?=.*? [XY])(?=.*? E)(?!;_WIPE)(?<!;_BRIDGE_FAN_START\n)(G1 .*?F)(\d+(?:\.\d+)?)/
+            $gcode =~ s/^(?=.*?;_EXTRUDE_SET_SPEED)(?!.*?;_WIPE)(?<!;_BRIDGE_FAN_START\n)(G1\sF)(\d+(?:\.\d+)?)/
                 my $new_speed = $2 * $speed_factor;
                 $1 . sprintf("%.3f", $new_speed < $self->min_print_speed ? $self->min_print_speed : $new_speed)
                 /gexm;
@@ -73,6 +73,7 @@ sub flush {
         $gcode =~ s/^;_BRIDGE_FAN_END\n/ $self->gcodegen->writer->set_fan($fan_speed, 1) /gmex;
     }
     $gcode =~ s/;_WIPE//g;
+    $gcode =~ s/;_EXTRUDE_SET_SPEED//g;
 
     return $gcode;
 }

xs/src/libslic3r/GCode.cpp

@@ -177,11 +177,11 @@ Wipe::wipe(GCode &gcodegen, bool toolchange)
             /*  Reduce retraction length a bit to avoid effective retraction speed to be greater than the configured one
                 due to rounding (TODO: test and/or better math for this)  */
             double dE = length * (segment_length / wipe_dist) * 0.95;
-            gcode += gcodegen.writer.set_speed(wipe_speed*60);
+            gcode += gcodegen.writer.set_speed(wipe_speed*60, gcodegen.enable_cooling_markers ? ";_WIPE" : "");
             gcode += gcodegen.writer.extrude_to_xy(
                 gcodegen.point_to_gcode(line->b),
                 -dE,
-                (std::string)"wipe and retract" + (gcodegen.enable_cooling_markers ? ";_WIPE" : "")
+                "wipe and retract"
             );
             retracted += dE;
         }
@@ -562,7 +562,7 @@ GCode::_extrude(ExtrusionPath path, std::string description, double speed)
     // extrude arc or line
     if (path.is_bridge() && this->enable_cooling_markers)
         gcode += ";_BRIDGE_FAN_START\n";
-    gcode += this->writer.set_speed(F);
+    gcode += this->writer.set_speed(F, this->enable_cooling_markers ? ";_EXTRUDE_SET_SPEED" : "");
     double path_length = 0;
     {
         std::string comment = this->config.gcode_comments ? description : "";