Dashboard takes ~1-2 secs for initial load, optimise initial view

[anchit-chandran]

Gut feeling for reason is because I'm doing a lot of compute inside the dashboard view (run all KPI calculate methods, then get all in the right format to send to all the htmx partials which will render the data in charts)

Reason is because CalculateKPIS needs the self.patients attr set, which is currently only done via one of the calculate_kpis_for_XXX methods, all of which set the appropriate .patients and then run all calculation methods. Instead, will refactor to setting pts in a separate method, so we can offload calculating only individual kpis in relevant htmx endpoints