Fix: Switching between multi-extruder printers using tabs can cause t…

[womendoushihaoyin]

Reproduction steps for the issue:

1. Select multiple multi-tool printers at once. （eg: prusa x5l / Snapmaker j1/Artisan）
   
2. Switch to another multi-tool printer using the tab.
   

you can observe that only one tool remains. Moreover, for multi-tool machines, Orca no longer allows the addition or removal of filament buttons (default). This can be very confusing for users.

Analysis：

1. In Orca, there is an inconsistency in how the extruder_count is determined for multi-tool printers. Some parts of the code use nozzle_diameter to determine the number of extruders, while others use extruder_colour
   . This inconsistency can lead to confusion and errors in the user interface, such as the addition or removal of filament buttons not being available for multi-tool machines, which will be perplexing.

To address this issue and align with the characteristics of printers like Prusa and Snapmaker, it is recommended to standardize the determination of extruder_count by using nozzle_diameter for parsing across the software. This approach would ensure a unified method for identifying the number of extruders, thereby reducing confusion and improving the user experience.

2. In multi-tool scenarios, modify the parameters passed to on_filaments_change.

3. prevent crashing