Optimized stats aggregation code for Admin dashboard

this code takes the API output and reduces it down to collect together stats per date
the current code is recursive, and we've seen errors with the recursion hitting a RangeError: Maximum call stack size exceeded error
as well as that, we're doing a lot of array concat'ing and cloning, which burns memory and CPU time
instead, we can just use .reduce
the new implementation is much faster than the existing one (1ms vs 85ms) and uses no recursion, so those errors should go away
I've also verified that the output is the same between the two functions

This should prevent long recursion chains like this: CleanShot 2024-06-26 at 14 28 01@2x

TryGhost / Ghost