Allow control of whether to return cached or freshly calculated formula values

[cfsimplicity]

By default, when reading formula cells, the formula will be evaluated to ensure you are getting an up-to-date result. But formula results are cached in the sheet and sometimes it may be useful/performant to skip recalculation and just grab the cached value.

Implement as a global library switch that can be turned on and off rather than yet another argument to the many methods that would need it.

[cfsimplicity]

Example usage:

data = spreadsheet
  .setReturnCachedFormulaValues( true )
  .read( src=path, format="query" );