fix: parse vulkan VRAM from text

[eglia]

Description
This PR fixes the vulkan VRAM parsing. As far as I can tell, the current implementation is nonsense, because vulkaninfo --json does not write to stdout:

[-j, --json]         Produce a json version of vulkaninfo output conforming to the Vulkan
                     Profiles schema, saved as 
                     "VP_VULKANINFO_[DEVICE_NAME]_[DRIVER_VERSION].json"
                     of the first gpu in the system.

Also, on my machine the json info did not actually contain the heap information, which is present in the text output.
This PR therefore changes to vulkaninfo --text and parses the output. On my 32GB AMD GPU, this correctly detects the available VRAM.
New output:
Total available VRAM vram=34208743424 caller={caller.file="/build/pkg/system/state.go" caller.L=79 }
Old output:
Total available VRAM vram=0 caller={caller.file="/build/pkg/system/state.go" caller.L=79 }

This PR fixes #9289

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