CWSimulator.write_sft_files does not generate random SFTs by default

Description of problem

When using CWSimulator.write_sft_files() to generate random Gaussian noise or injections in Gaussian noise, by default, different trials do not produce random noise.

The parameter "noise_seed" is set to 0 by default. If we input random seeds into that noise_seed, the output SFTs from different trials become random. But if we keep noise_seed=0, the output SFTs are almost identical; "almost identical" means that the first SFT in a sequence is random, but starting from the second one and onwards, the SFTs are identical from multiple trials, i.e., SFT(0)_trial0 != SFT(0)_trial1, but SFT(n)_trial0 = SFT(n)_trial1 when n>0.

Expected behavior

By default, the Gaussian noise generated should be random. If we run 100 trials, that should represent random Gaussian noise.

Steps to reproduce

Some dummy code here:

    S = CWSimulator ( tref=args.tref,
                      tstart=args.t0,
                      Tdata=args.T,
                      waveform=wf,
                      dt_wf=args.dtwf,
                      phi0=args.phi0,
                      psi=args.psi,
                      alpha=args.ra,
                      delta=args.dec,
                      det_name=detector,
                      tref_at_det=True,
                      extra_comment = cmdline
                    )

  S.write_sft_files ( fmax=args.sft_fmax,
                      Tsft=args.sft_T,
                      comment="simulation",
                      noise_sqrt_Sh=args.noise_sqrt_Sh,
                      out_dir=sft_out_dir,
                      window=args.sft_window,
                      window_param=args.sft_window_param
                   )

Problem can be solved by adding noise_seed=random.randint(0,100000) to S.write_sft_files()

Context/environment

This was found when running simulations for short-duration vector boson signals on CIT clusters (also on personal laptop). The same issue exists for whatever simulations done in Gaussian noise.