mipmap are not applied at runtime load glb file

### Tested versions

4.3 stable

### System information

Windows 11 - Godot 4.3 Stable

### Issue description

1. editor imported *.glb model - mipmap ok
2. separate model (*.gltf+*.bin+*.png) - mipmap ok
3. embed texture model (*.glb) - mipmap not ok

When loading a glTF file with embedded textures at runtime, mipmaps are not applied. I tried using the `GLTFState.get_images()` function to retrieve the images, calling the `generate_mipmap` function on them, and then resetting them with `GLTFState.set_images`, but it still doesn't work.

Looking through past issues, it seems that mipmaps are not applied to glTF files with embedded textures. Is there any plan to support mipmap generation for *.glb files with embedded textures when loaded at runtime?

I couldn’t find anything related in the milestones.

best regards.

### Steps to reproduce

```gdscript
extends Node3D

var loaded_model

func _ready() -> void:
var gltf_document = GLTFDocument.new()
var gltf_state = GLTFState.new()

var error = gltf_document.append_from_file("res://Model/TestModel.glb", gltf_state)
if error == OK:
# generate mipmap
var images = gltf_state.get_images()
var new_images_array = []
for img in images:
var src_img = img.get_image()
src_img.generate_mipmaps()
new_images_array.append(ImageTexture.create_from_image(src_img))
print("src_img.get_size() -> ", src_img.get_size())
print("src_img.get_mipmap_count() -> ", src_img.get_mipmap_count())
gltf_state.set_images(new_images_array)

loaded_model = gltf_document.generate_scene(gltf_state)
add_child(loaded_model)
```

### Minimal reproduction project (MRP)

[mipmaptest.zip](https://github.com/user-attachments/files/18154749/mipmaptest.zip)

Run the linked mipmaptest.zip reproduction and trace the shown GLTFDocument.append_from_file, GLTFState.get_images/set_images, and generate_scene calls. Compare runtime loading of embedded-texture GLB files with separate glTF assets, then verify that generated scenes retain mipmaps for embedded textures.

Written by the indexing model from the issue text.