Memoisize stats function

[NeuroShepherd]

Inputs are likely to be repeated many times over either in a Shiny session or when using the function directly. For performance improvement, consider using {memoise}

[NeuroShepherd]

Unclear if {memoise} can cache across parallel sessions, but {R.cache} apparently is capable of this.

[NeuroShepherd]

As an additional comparison note between {memoise} and {R.cache}:

• The former caches data in-memory in the current session which is faster to write to and access, but can clog up the session if there's too much happening. Additionally, the results are stored only transiently.
• R.cache caches the data to a file outside of the session. There is a higher overhead to writing and reading this data, but allows access across multiple sessions and in parallel processes.