fix: track charges on deisotoped ions (#220)

[lazear]

Tracks charge state per ion in ProcessedSpectrum as a SoA charges: Vec column (#220)

• Preserves reassigned charge state for deisotoped MS2 peaks (otherwise defaults to 1)
• Removes the transient spectrum::Peak AoS helper
• Updates matched fragment annotation so fragment_charge, calculated m/z, and experimental m/z reflect the observed/deisotoped peak charge