PERF: increase the minimum number of elements to use numexpr for ops from 1e4 to 1e6
See https://github.com/pandas-dev/pandas/issues/40500 for the analysis.
prob need to update the docs a bit here https://pandas.pydata.org/docs/user_guide/enhancingperf.html > prob need to update the docs a bit here https://pandas.pydata.org/docs/user_guide/enhancingperf.html

That page is about using numexpr in `eval`/`query`, so that is independent from this change. On the basic page is a section about accelerated ops: https://pandas.pydata.org/docs/user_guide/basics.html?highlight=numexpr#accelerated-operations 
But it doesn't mention the minimum number of items, so that doesn't need to be updated (we should update the table id at some point switching to the ArrayManager, as that will be influenced, but so that's still for the future) Looks like this wasnt green when merged, could be responsible for broken CI?