Provide a different calculation method for StateAgeFunctions for minimal boost version

[lenaploetzke]

Feature description

If only the minimal boost version is used (see issue #992) and the boost functions for epidemiology/state_age_function.h cannot be used, one could offer the possibility to approximate the cdf via a numerical approximation of the integrals. The functions of boost are mostly optimised for runtime, and the eval() functions involved determine the runtime of our program, so the numerical approximation is not the preferred solution.

Additional context

No response

Checklist

• [X] Attached labels, especially loc:: or model:: labels.
• [X] Linked to project.

[lenaploetzke]

Downloading boost is now faster and it is no longer planned to include a minimal version of boost (see #992). This issue is therefore outdated.