implement SpecLibFlat.remove_unused_fragments()

[GeorgWa]

Currently, remove_unused_fragments is only implemented for dense libraries. An implementation for flat libraries would be very usefull and should be easy to implement.

[jalew188]

I think we already have args frag_start_col and frag_stop_col for different cases, see https://github.com/MannLabs/alphabase/blob/main/alphabase/peptide/fragment.py#L867

[jalew188]

I designed this for spectrum_df's peak_start_idx and peak_stop_idx, flat_lib case should be similar

[GeorgWa]

I agree, it's most likely a very simple function and we can use https://github.com/MannLabs/alphabase/blob/main/alphabase/peptide/fragment.py#L867

[jalew188]

Is this issue still required? @GeorgWa

[GeorgWa]

It was implemented in #149 👍