Spread work more evenly between threads

[ianopolousfast]

Vectorize skipping first partial line

Check List:

• [X] You have run ./mvnw verify and the project builds successfully

• [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

• [X] 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: 11.6s on 4 core i7 (.4s faster)

• Execution time of reference implementation: 288s

[gunnarmorling]

Also not a measurable improvement:

Benchmark 1: timeout -v 300 ./calculate_average_ianopolousfast.sh 2>&1
  Time (mean ± σ):      4.809 s ±  0.032 s    [User: 34.389 s, System: 0.749 s]
  Range (min … max):    4.781 s …  4.860 s    5 runs

Summary
  ianopolousfast: trimmed mean 4.800795321993334, raw times 4.78106628766,4.81001773666,4.860319667660001,4.80970452866,4.782663700660001

Leaderboard

| # | Result (m:s.ms) | Implementation     | JDK | Submitter     | Notes     |
|---|-----------------|--------------------|-----|---------------|-----------|
|   | 00:04.800 | [link](https://github.com/gunnarmorling/1brc/blob/main/src/main/java/dev/morling/onebrc/CalculateAverage_ianopolousfast.java)| 21.0.1-open | [Dr Ian Preston](https://github.com/ianopolousfast) |  |