improved 2nd and final submission

[yourwass]

• eliminated memory allocations on the hot path
• used serkan-ozal's trick to exclude munmap from timings

Check List:

• You have run ./mvnw verify and the project builds successfully
• Tests pass (./test.sh <username> shows no differences between expected and actual outputs)
• All formatting changes by the build are committed
• 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
• For new entries, or after substantial changes: When implementing custom hash structures, please point to where you deal with hash collisions (line number): 216

• Execution time: 10-15% better than my 1st submission
• Execution time of reference implementation: