Fix deadlock in stdio.format calls in tostring metamethod

[daimond113]

Fixes a deadlock when calling stdio.format in a __tostring metamethod in a function such as print, which internally formats using the same function as stdio.format.

Fixes #273.

[filiptibell]

I think this is good enough to solve this specific issue for now - thank you! In the future we should probably roll our own ansi formatter instead of relying on a third party crate and its global state/config, which would also resolve this.