Physics improvements

[kpedro88]

• Add 3-body decays for $\rho_{\mathrm{dark}}$
• Simulate the actual Z′ width based on quark and dark quark coupling values
• Improve mass insertion decays for $m_{\pi_{\mathrm{dark}}} < 2m_{\mathrm{c}}$ by using bound states (e.g. from https://gitlab.com/simonknapen/dark_showers_tool)
• Add lifetime/ctau parameter for emerging jet simulations
• Update Delphes card with newer/more up-to-date CMS resolutions