Allow model to handle weekly (or any specified interval) count data

[kaitejohnson]

Goal

Currently the model expects daily count data, and we have set it up to throw an error if this is not the case. However, we should be able to let the user specify that the count data is not daily, and then sum up the daily latent hospital admissions to get aggregated to whatever interval (most likely weekly, but this could be configurable).

Tasks

• modify wwinference to let the user specify the temporal granularity of the data
• modify wwinference.stan to aggregate between non successive hosp_times if the user specifies an interval for aggregation (otherwise, a missing hosp time is treated as unobserved)
• write tests for both cases, consider including an example in vignette (though this might be a separate vignette where we demonstrate advanced options?)