Draft: BandQ development for 2025 first reoptimisation

Aiming for %Reoptimised Hlt2 selections for 2025: "lossless" first pass.

This MR should be ready around 1 week before December LHCb week.

Please create an MR targetting on bandq_development and ping Yajing and Mengzhen for review.

Using Hlt/Hlt2Conf/options/examples/bandq/HLT2_bandq_example.py to test the bandwidth.

Existing updates:

• added 6 Xib0, Xib-, Omb- decay modes (resolving #879 (closed))
• fixed am_min 5780 -> 5580 in Xib lines including general function make_xib2cx_for_spectroscopy
• added shortcut functions tight_track (as in bandq_EoY_sprucing), charm_dm and Cst_or_tight_track
• added Bc pt cut (!4090)