Split uploaded combat logs into parts#15

Combat logs are actually multiple csv files stitched together into one file, separated by empty lines. Before we can parse the csv, we have to split it into the individual sub-components. Each one has its own schema. This does no csv parsing yet, it just splits up the raw log file. I had to refactor the service tests in order to be able to test this new functionality and replaced Jest with NodeJS's built-in test runner because I finally reached a dead-end with the fragile build configuration I was using where production code was being transpiled by tsc into JavaScript *before* being run, while test code was getting transpiled on-the-fly by tsx without producing any JavaScript output files. Now, everything gets transpiled by tsc, and node runs the JavaScript.