Allow specifying on CLI the number of lines to load from a file

[jwnacnud]

If I have a large file, certainly I can just HEAD it to get the lines I want. I'd love to run the following:

vd -n100000 filename.csv

and have visidata simply open the first 100,000 records of the file. I know I can ctrl-c to stop along the way on a large file but that's not consistently stopping in the same place. I also know that I can head the file, if the file supports that, which parquet doesn't.

Am I just dreaming?

• [X] what should the helpstring say This value indicates how many records will be loaded from the input file (default, all of them)
• [X] where should this command go in the menu system ON INPUT, not in the menu system.