Add a worked tutorial for the XRB luminosity utilities

Context

PR #881 adds small property-based XRB utility functions with complete API docstrings and literature references. The API reference can therefore be generated automatically, but it does not replace a worked scientific tutorial.

Proposed tutorial

Add a population-synthesis tutorial that demonstrates:

• selecting bound BH/NS systems with non-compact donors;
• mapping POSYDON S1/S2 columns to donor and accretor properties;
• distinguishing RLO, wind-fed, and Be-XRB systems;
• calculating BH/NS efficiencies, Eddington quantities, wind capture, classical luminosities, and King beaming;
• applying observational band corrections outside the utility module;
• constructing a weighted cumulative XLF; and
• documenting assumptions and deferred physics such as GRRMHD, magnetic NS accretion, and wind-disc formation.

The tutorial should be executable with a documented POSYDON version and a small registered example dataset. It should be reviewed separately from #881.