Extend libnest tests, remove some warnings, faster catch2 compilation.

Also, improve libnest2d::nest interface.

src/libslic3r/Arrange.cpp

@@ -375,7 +375,7 @@ public:
         
         for(unsigned idx = 0; idx < fixeditems.size(); ++idx) {
             Item& itm = fixeditems[idx];
-            itm.markAsFixed();
+            itm.markAsFixedInBin(0);
         }
 
         m_pck.configure(m_pconf);