remove stats_ from output filenames

[madjin]

instead of stats_2025-02-09.json just do 2025-02-09.json, makes CI easier for other workflows + its redundant since its in the stats folder

[META-DREAMER]

I think its better to keep it like it is since if the file gets copied and used outside of that folder, you still know what it is vs just a date wont tell you much. How exactly does it make CI easier? isnt it trivial just to prepend stats_?