SpectrumProcessor saving of spectra should maybe be one by one

[florian-huber]

Currently the SpectrumProcessor will first process all spectra (self.process_spectrum) and only at the end write them to file (save_spectra(processed_spectrums, cleaned_spectra_file)).

For larger workflows this seems not ideal because it can crash at a very late stage (just happened to me...).
I think it would be better to write each spectrum to the file once processed, at least for formats where this is possible such as .msp and .mgf.

[hechth]

I agree - this is also already possible with the streaming write we implemented for those formats - we should add the json implementation though at some point.