win: fix patch-tester

[Bertaz]

Current command doesn't work. This error is always returned:

[hwupload @ 000001f89307f4c0] A hardware device reference is required to upload frames to.
[AVFilterGraph @ 000001f89303f380] Error initializing filters
Error opening output file -.

Updated ffmpeg command as per documentation ffmpeg.org hwaccel -init_hw_device.
Fixes #892, fixes #1070

[Bertaz]

On systems with multiple cuda capable GPUs it's possible that -init_hw_device cuda complains, probably best to add cuda:0. I'll test if it gives any problem on my single GPU PC.

Additionally the -t 50 at the end is misplaced, the intention was probably to stop the rendering after 50s. But it only works if placed before the -i input. Even better it should be testsrc=duration=50 as per documentation.

Also testsrc complains on latest ffmpeg, as it gives rgb24 pxfmt to h264_nvenc, which accepts only YUV formats. Should use testsrc2 instead.
Tested and it works on latest, 8.1, 7.1 and self compiled ffmpeg from 2025.

[Bertaz]

Tested cuda:0 and it works with single GPU systems and multiple GPUs (selecting the first one). It also surfaces the option to select a specific GPU.

Changed to duration for the source input instead of general duration.
Increased video duration to 150 seconds.
50 seconds on beefy computers can be too quick for the user to see the messages. No issue on slower computers as it was infinite before.

Last commit can be dropped it it's unwanted.