nsteps is incorrectly obtained from the NetCDF file

[IAlibay]

When calculating dt, the value for nsteps is read from online_analysis_interval which is incorrect.

See:

openfe_analysis/src/openfe_analysis/reader.py

Lines 23 to 29 in 484938b

	option_data = ds.variables['options'][0].split('\n')
	for line in option_data:
	if line.startswith('online_analysis_interval'):
	nsteps = float(line.split()[-1])
	break
	else:
	raise ValueError("Didn't find online_analysis_interval")

Instead it should just be calculated from the move value in the same way we do for timestep.

I.e.

for line in nc_dataset.groups['mcmc_moves']['move0'][0].split('\n'):
    if lline.split(':')[0] == 'n_steps':
        nsteps = int(line.split(':')[1])