Formatting in dump file

[mphoward]

The formatting in a dump file is hard-coded:

lammpsio/src/lammpsio/dump.py

Lines 153 to 156 in 064e823

	elif key in ("position", "velocity"):
	fmt = "{:.8f}"
	else:
	fmt = "{:f}"

but does not match what is currently specified as the default by dump modify:

https://docs.lammps.org/dump_modify.html

I think we should change the default format string for floats to be :g for consistency. In addition, it might be nice to add an option to set a format string for keys in the schema if the user wants to override this default behavior.

There is likely a similar issue with the data file, but LAMMPS is less clear about what formatting it uses. We might consider addressing that in a separate issue.