[aaronkanzer]

Reading an MGF spectrum whose RTINSECONDS is a range raises, and the rest of the file cannot be read:

BEGIN IONS
TITLE=Spectrum 3
PEPMASS=1244.7
SCANS=29-34
RTINSECONDS=95-97
100 1
END IONS

next(mgf.read("rtrange.mgf"))
# ValueError: could not convert string to float: '95-97'

This spectrum is the example in the Mascot MGF documentation (https://www.matrixscience.com/help/data_file_help.html). Its parameter table defines RTINSECONDS as "Retention time or range (in seconds)", a[-b], and the merged peak list section allows "a single retention time to a complex list of retention time ranges". Mascot Distiller writes ranges for summed scans.

Why: _read_spectrum_lines always runs aux.unitfloat(params['rtinseconds'], 'second').

Fix: convert only when the value is a single number. Otherwise keep the string as given, the same way SCANS ranges are kept.

Tested:

• New test_rtinseconds_range checks that both MGF and IndexedMGF read a range and a single value. It fails on master and passes with the fix.
• Full suite: 467 passed before, 468 passed after (same 10 sandbox-only map() failures).
• No change on real files: 32,691 spectra and 2,071,884 peaks (38 GNPS libraries, 17,091 Enveda-180 spectra, and the pyteomics and matchms MGF test data) give the same hash (7ff3778b69f55a99) before and after.