Preserve loaded filament palette when importing colored 3MF files

[gigq]

Summary

This changes colored 3MF import so the app keeps the user's currently loaded physical filaments instead of replacing them with the colors embedded in the 3MF project.

When a colored 3MF is imported, the importer now:

• reads the target filament colors from the file
• approximates those targets using the currently loaded physical filament palette
• creates/reuses virtual mixed filaments for the imported colors
• remaps imported model extruder assignments to those physical or virtual filament IDs

This also fixes a UI refresh issue where physical filament swatches could stay stale after import when the filament count did not change, and refreshes mixed filament display colors for manual-pattern entries.

Why

Before this change, importing a colored 3MF could overwrite the visible filament colors in slots 1-4 with the file's palette, even when the user wanted to keep a fixed physical palette loaded and approximate the model colors from that palette.

That caused the sidebar swatches, multicolor preview, and actual print intent to drift apart.

What changed

• preserve the existing physical filament palette during colored 3MF import
• synthesize imported colors into mixed virtual filaments instead of replacing slots 1-4
• remap imported model extruder assignments onto the synthesized physical/virtual filament IDs
• refresh physical filament combo swatches even when the filament count stays the same
• refresh mixed filament display colors for manual-pattern entries
• normalize imported 8-digit hex color values to RGB before matching

Notes

This is a heuristic color approximation based on the currently loaded palette. It improves import behavior for fixed-palette workflows, but it is not a full physical pigment/translucency model and does not guarantee exact printed color matching.

[gigq]

Here is the results from a CYMK print of Yoshi, after importing it will auto add the colors from the 3mf file so no need to calculate or guess at the best mix.