feat(libslic3r): multi-nozzle slicing engine for H2C/A2L

Port BambuStudio's dual-nozzle slicing core: H2C-era config keys, filament-to-nozzle grouping with per-layer dynamic regrouping, filament/nozzle/hotend gcode placeholder vocabulary, multi-nozzle wipe tower pre-heat/pre-cool, the two-pass pre-cooling injector, and corexy farthest-point timelapse.

src/libslic3r/utils.cpp

@@ -8,6 +8,10 @@
 #include <iostream>
 #include <stdio.h>
 #include <filesystem>
+#include <sstream>
+#include <iomanip>
+#include <algorithm>
+#include <cmath>
 
 #include "format.hpp"
 #include "Platform.hpp"
@@ -1497,6 +1501,15 @@ std::string format_memsize(size_t bytes, unsigned int decimals)
 		}
 }
 
+std::string format_diameter_to_str(double diameter, int precision)
+{
+    double candidates[] = {0.2, 0.4, 0.6, 0.8};
+    double best = *std::min_element(std::begin(candidates), std::end(candidates), [diameter](double a, double b) { return std::abs(a - diameter) < std::abs(b - diameter); });
+    std::ostringstream oss;
+    oss << std::fixed << std::setprecision(precision) << best;
+    return oss.str();
+}
+
 // Returns platform-specific string to be used as log output or parsed in SysInfoDialog.
 // The latter parses the string with (semi)colons as separators, it should look about as
 // "desc1: value1; desc2: value2" or similar (spaces should not matter).