Triplanar with different colorspaces gets wrong color transform

### Description

When using the `` node (which has 3 filename inputs) and different colorspaces on the different inputs only one colorspace transform is generated.

### To reproduce

Create a `` node with different colorspaces on the different input and observe the generated OSL code.

[repro-triplanar.zip](https://github.com/user-attachments/files/18396033/repro-triplanar.zip)

### Result
Generated OSL code:
```
NG_triplanarprojection_color3(triplanarprojection_filex_, triplanarprojection_filey_, triplanarprojection_filez_, triplanarprojection_layerx, triplanarprojection_layery, triplanarprojection_layerz, triplanarprojection_default, geomprop_Pobject_out1, geomprop_Nobject_out1, triplanarprojection_upaxis, triplanarprojection_blend, triplanarprojection_filtertype, triplanarprojection_framerange, triplanarprojection_frameoffset, triplanarprojection_frameendaction, triplanarprojection_out);
color triplanarprojection_out_cm_out = color(0.0);
NG_srgb_texture_to_lin_rec709_color3(triplanarprojection_out, triplanarprojection_out_cm_out);
```

### Expected result
I'd expect that three colorspace transforms would be emitted, one for each file input, with the corresponding source colorspace for each file input.

Start with the attached repro-triplanar.zip and inspect the generated OSL for a triplanarprojection node with three differently colored inputs. Trace the triplanarprojection code-generation entry point and existing colorspace-transform handling, then verify that the generated output contains one transform per file input with its source colorspace.

Written by the indexing model from the issue text.