Fix df.count() behavior to perform count_rows instead

[jaychia]

Is your feature request related to a problem? Please describe.

When users run df.count(), they often expect df.count_rows() behavior. Instead, df.count() will perform a count aggregation on every column, which is not the intended behavior.

Interestingly, Spark returns an int for the .count() operation, which is perhaps most intuitive.

See Spark behavior: https://saturncloud.io/blog/counting-rows-in-pyspark-dataframes-a-comprehensive-guide/#counting-rows-using-the-count-function

We should discuss the intended behavior for our df.count() operation and implement a fix.

[universalmind303]

Coming from other dataframe libraries, this has tripped me up several times.

+1 to changing the behavior

[samster25]

Yeah it's a common confusion point. I think its finally time!