Tiling LPE gaps are not exported correctly to PDF
#### Summary:
The `Tiling` Live Path Effect's `Gap` distances are not exported correctly to PDF unless px is used as distance unit. Every other unit lead to a smaler gap size in the resulting PDF. Export to PNG results into a correct image.
#### Steps to reproduce:
1. Open Inkscape
2. Create a rect 10x10 mm at top left X/Y position 10 mm
3. Add a `Tiling` LPE to the rect with 3 rows and 3 columns and X/Y gap size of 1 mm
4. Create a surrounding rect 34x34 mm at top left X/Y position 9 mm
5. Export the document to PNG and PDF
6. Compare the X/Y gap distances between the two output formats and observe the much smaller X/Y gaps in the PDF output
7. Change the gap distance unit of the `Tiling` LPE to `px`, export to PDF again and observe the correct gap distance in the PDF output
#### What happened?
It looks like Inkscape exports the tiling gap distance to PDF wrongly for every distance unit except `px`. The exported gap distance is different for the other units. It seems to be that Inkscape converts the gap distances again/wrongly during export.
#### What should have happened?
The gap distances should be correctly exported to PDF regardless of the used gap distance unit. The output should be comparable to the PNG output.
Sample attachments:
See the attached the sample file highlighting the issue.
{width=129 height=129}
[TilingLPE_Gaps.pdf](/uploads/57ae404e8861143b633391eb3868b22c/TilingLPE_Gaps.pdf)
#### Version info
```
Inkscape 1.4.4 (dcaf3e7, 2026-05-05)
Compile (Run)
GLib version: 2.86.3
GTK version: 3.24.51 (3.24.51)
glibmm version: 2.66.8
gtkmm version: 3.24.10
libxml2 version: 2.15.1
libxslt version: 1.1.45
Cairo version: 1.18.4 (1.18.4)
Pango version: 1.56.4 (1.56.4)
HarfBuzz version: 12.2.0 (12.2.0)
OS version: Windows 11 25H2
```
issue