feat: radius for LinearProgressBar

[nickf2k]

hi @maravilho, @maravilhosinga I used your package. It's great.
However, I think adding a radius to the LinearProgressBar would be a nice improvement, similar to this

or this

Can I open a PR for this issue?

[maravilhosinga]

Hello, @nickf2k
You can open PR.

I'm a little busy right now. I will make some updates when possible, but you are free to contribute.

[nickf2k]

@maravilhosinga I open a PR for this at here #2