Writes results_df (a data frame/tibble summary produced by
build_simulation_result()) to path as a parquet file using
nanoparquet. The data frame is coerced to a plain data.frame first so
that tibble/vctrs columns parquet cannot represent are flattened.
Details
Requires the suggested nanoparquet package; if it is not installed,
rlang::check_installed() prompts (or errors) accordingly.