Add Table `zip_columns` method for faster row iteration

One way to substantially improve performance when iterating over rows is to avoid explicit use of Row for access. Instead of:

for row in tbl:
   function(row['a'], row['b'], row['z'])

Do:

for a, b, z in zip(tbl['a'], tbl['b'], tbl['z']):
   function(a, b, z)

This is much faster because it ends up using C-level iteration instead of a lot of Python code to make a Row and then access it.

In many cases of iterating over table rows, one only cares about a small subset of the column values. So we can make the above nicer with:

for a, b, z in tbl.zip_columns('a', 'b', 'z'):
   function(a, b, z)

One question is if the name is confusing. Technically it should be called zip_columns, but I’m not sure that would make more sense to the average user. [Changed to zip_columns].

@himanshupathak21061998 - this might be a good straightforward table performance issue to try.

[geekypathak21]

Sure, I will try to fix this.

[mhvk]

Agreed - zip_columns is useful regardless - it also helps make sure the columns are zipped in an explicit order.