use i32 rather than u32 for workspace ids

[Atemu]

Hyprland's special workspaces have negative indices which would cause i3bar-river to irrecoverably display an error.

I built this before I looked whether someone else already did this and found https://github.com/MaxVerevkin/i3bar-river/pull/47/.

I think I like not filtering out workspaces at all to be the better option because this way the special workspace is shown in front of the other workspaces but only when it's activated which I find quite intuitive; it's special afterall.

This behaviour is infinitely better than irrecoverably soft-crashing either way.

Fixes https://github.com/MaxVerevkin/i3bar-river/issues/46