libslic3r: Fix format calls

src/libslic3r/Support/TreeSupport.cpp:3204:41: error: ‘format’ was not declared in this scope; did you mean ‘boost::format’?
 3204 |             BOOST_LOG_TRIVIAL(trace) << format("plan_layer_heights0 (%.2f,%.2f)->(%.2f,%.2f): ", z1, h1, z2, h2);
      |                                         ^~~~~~
      |                                         boost::format

src/libslic3r/Support/TreeSupport.cpp

@@ -2,6 +2,7 @@
 #include <chrono>
 #include <math.h>
 
+#include "format.hpp"
 #include "ClipperUtils.hpp"
 #include "Fill/FillBase.hpp"
 #include "I18N.hpp"