minimum data.table

[sbfnk]

turns out this line in the new non-randomised PIT

https://github.com/epiforecasts/scoringutils/blob/07610998f9ec35e32b4510e3bee7fd8681a0ade3/R/metrics-sample.R#L582

relies on a fairly cutting-edge data.table version (1.16.0, released 25 August 2024) that supports a vector for default

We either have to require this version as a minimum or change the code.