Use parquet list schema for stacktraces

[simonswine]

This is a cosmetic change. (Even before things were store, but not displayed correctly using thrid party tooling).

This is how it looks like now:

$ pqrs cat data/head/01G7XRZFHP796NF04E7XX7SDMM/stacktraces.parquet | head -n 5

##############################################################
File: data/head/01G7XRZFHP796NF04E7XX7SDMM/stacktraces.parquet
##############################################################

{ID: 0, LocationIDs: [0, 1, 2, 3, 4, 5, 6, 7, 2, 8, 2, 9, 2, 10, 2, 11, 12, 2, 13, 14]}
{ID: 1, LocationIDs: [15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35]}
{ID: 2, LocationIDs: [36, 37, 38, 39, 40, 41]}
{ID: 3, LocationIDs: [42, 40, 41]}
{ID: 4, LocationIDs: [43, 44, 45, 46, 47, 48, 49, 23, 24, 25, 26, 27, 28, 29, 30, 31, 50, 51, 34, 35]}