ENH: to_csv and read_{fwf/csv/table} type improvements

[bashtage]

• Tests added: Please use assert_type() to assert the type of any return value

[bashtage]

@Dr-Irv Looks like the loguru stuff fixed itself?

[bashtage]

Maybe not fixed, but random. Might depend on the CI worker node.

[Dr-Irv]

Maybe not fixed, but random. Might depend on the CI worker node.

Yes, this randomness is part of the problem. I don't know what to do about it.

[Dr-Irv]

My only concern here is that I can't tell if you modified read_csv() or read_table() because they moved from one file to the other.

If you did change read_csv() or read_table(), can you do one PR that just modifies their signatures, but keeping them in the same file, so it is easy for me to compare what you changed, and then a second PR that moves them from where they are in main now to the new place you put them.

[bashtage]

If you did change read_csv() or read_table(), can you do one PR that just modifies their signatures, but keeping them in the same file, so it is easy for me to compare what you changed, and then a second PR that moves them from where they are in main now to the new place you put them.

Created #248 in place of this