Added improvments on string copying, string comparation & calculation of next index in case of collision in custom map

[JaimePolidura]

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)

• Execution time: 3s - 4s
• Execution time of reference implementation: 2 min - 3 min

[gunnarmorling]

00:04.101 now.

[JaimePolidura]

great, thank you :)