fatroom 2nd attempt: lazy strings init, custom station map

[fatroom]

Delay string init as much as possible.

Check List:

• [x] Tests pass (./test.sh <username> shows no differences between expected and actual outputs)
• [x] All formatting changes by the build are committed
• [x] Your launch script is named calculate_average_<username>.sh (make sure to match casing of your GH user name) and is executable
• [x] Output matches that of calculate_average_baseline.sh

• Execution time: 10s
• Execution time of reference implementation: 4m