J-Sek implementation (Bun workers)

[J-Sek]

Check List:

• Tests pass (./test.sh <username> shows no differences between expected and actual outputs)
• All formatting changes by the build are committed (?? I am not sure what it means ??)
• Your launch script is named calculate_average_<username>.sh (make sure to match casing of your GH user name) and is executable
• Output matches that of calculate_average_baseline.sh

• Execution time: ~45s (with i5-13600KF / 20 threads) around 3x more than @janlucaklees's implementation 😅
• Execution time of reference implementation: 4m 56s