fix: always add model name to experiment run

[paoloricciuti]

I think it's nice to split the results by model to keep them organized...we should also add the model to the result imho

[gaojude]

cc @allenzhou101 this might break result parsing for playground UI due to changes to folder structure

[paoloricciuti]

If you think could be considered a breaking change for some people we can push this over (or use a minor instead of a patch to signal that)

[paoloricciuti]

Oh actually I thought playground was just a playground app...just now I realize is actually a package...let me also update that

[paoloricciuti]

And btw this was already possible before...but only when multiple models were used...this PR just unify the behavior (which is also better for the playground because it doesn't have to check multiple kind of paths...even tho since models have slashes in them it will create folders which is a bit annoying)

[paoloricciuti]

Fixed the playground...here's how it looks like in my test

Please let me know if I should remove the model name from the experiment in the playground (but i think it's actually pretty nice you can have that)

[gaojude]

Lgtm