Allow longer bandwidth lines in bandwidth files

Bandwidth files have a line limit of 510 characters (512 - newline and NUL).

We should make sure this limit is high enough for future bandwidth files.

We can do this by finding out the current length of sbws and torflow lines, multiplying it by 4x, then rounding up to the nearest power of two.

We can use the examples in the spec if we need to: https://gitweb.torproject.org/torspec.git/tree/bandwidth-file-spec.txt

Maybe we should wait until sbws has added all the new fields?