Keep instance of sysinfo System struct

[Small-Ku]

Not really a fix but I see sysinfo recommends keeping this struct.

Another issue frequently encountered: unless you know what you're doing, it's almost all the time better to instantiate the System struct once and use this one instance through your program.
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Another example why it's much better: in case you want to list all running processes, sysinfo needs to allocate all memory for the Process struct list, which takes quite some time on the first run.

They also disable multithread feature by default since 0.34 because of GuillaumeGomez/sysinfo#1352. Since we don't use sysinfo in Linux, I re-enabled it in lib\Cargo.toml.

[SpikeHD]

Nice! Thank you!