Add From<&EcoString> for EcoString impl

[idlercloud]

Add an impl like impl From<&String> for String to allow convert &EcoString to EcoString. In my use case, this will enable function to take param as impl Into<EcoString>, so it can receive either &EcoString or EcoString.

[laurmaedje]

I'm not a huge fan of this as it could hide unnecessary clones where a move would be possible. But I guess consistency with std is more important.

[idlercloud]

Sorry for accidentally committing irrelevant code. I have revert it.

Since std already did this, it looks ok for us to do the same.

However, I briefly investigated other string optimization crates in the ecosystem, and it seems that none of them implement this.

Considering that cloning EcoString is cheap, for my use case, simply passing an EcoString seems to be acceptable.

So feel free to merge or reject.

[laurmaedje]

Let's follow std here rather than other third party crates.

I got to fixing CI so that we don't get a red checkmark on main after merge.

Thanks!