Refactor GCode handler variable and command line flag names

Renamed `gcode_prefix_handler_` to `gcode_header_handler_` for clarity. Updated corresponding usage in `EmscriptenCommunication.h`, `CommandLine.cpp`, and `EmscriptenCommunication.cpp`.

Contribute to NP-327

include/communication/EmscriptenCommunication.h

@@ -21,7 +21,7 @@ class EmscriptenCommunication : public CommandLine
 {
 private:
     std::string progress_handler_; ///< Handler for progress messages.
-    std::string gcode_prefix_handler_; /// <Handler for getting gcode_prefix.
+    std::string gcode_header_handler_; ///< Handler for getting the GCode handler.
     std::string slice_info_handler_; ///< Handler for slice information messages.
 
     /**

src/communication/CommandLine.cpp

@@ -192,7 +192,7 @@ void CommandLine::sliceNext()
                     force_read_parent = false;
                     force_read_nondefault = false;
                 }
-                else if (argument.starts_with("--progress_cb") || argument.starts_with("--slice_info_cb") || argument.starts_with("--gcode_prefix_cb"))
+                else if (argument.starts_with("--progress_cb") || argument.starts_with("--slice_info_cb") || argument.starts_with("--gcode_header_cb"))
                 {
                     // Unused in command line slicing, but used in EmscriptenCommunication.
                     argument_index++;

src/communication/EmscriptenCommunication.cpp

@@ -33,9 +33,9 @@ EmscriptenCommunication::EmscriptenCommunication(const std::vector<std::string>&
     {
         slice_info_handler_ = *ranges::next(slice_info_flag);
     }
-    if (auto gcode_prefix_flag = ranges::find(arguments_, "--gcode_prefix_cb"); gcode_prefix_flag != arguments_.end())
+    if (auto gcode_header_flag = ranges::find(arguments_, "--gcode_header_cb"); gcode_header_flag != arguments_.end())
     {
-        gcode_prefix_handler_ = *ranges::next(gcode_prefix_flag);
+        gcode_header_handler_ = *ranges::next(gcode_header_flag);
     }
 }