internal function to make list

[AugustHao]

• compute_infections
• estimate_delays: need to think about interface for time-varying and non-time-varying options, and moving window for calculating time-varying delays. Input data cannot be date agnostic, for the purpose of linking link-varying ascertainment delay with other time-varying delays
• make_incubation_period_cdf: can change input data in the future
• make_ecdf: auxiliary function, does not need to be user-facing
• combine_delay_ecdf: currently only numeric sampling method implemented but computationally cheaper method is proposed --- gain is likely trivial though
• constructor functions for empirical cdfs and pmfs, organised by days-of-delay
• aux functions to help populate the convolution matrix with the delay-mass-function-of-the-day