replace unnecessary Map with a List

[tyrasd]

implements suggestion from @rtroilo in #332 (comment)

Description

Replaces a not necessary usage of a (sorted) Map with a simple List. Should lead to slightly improved performance in some queries and reduced memory consumption.

Checklist

• My code follows the code-style rules, and I have checked on the static analyses and benchmark (if applicable) results
• I have commented my code
• I have written javadoc (required for public methods)
• I have added sufficient unit tests
• I have made corresponding changes to the documentation
• I have updated the CHANGELOG.md
• I have adjusted the examples or created an issue in the corresponding repository
• I have adjusted the benchmark or created an issue in the corresponding repository

[tyrasd]

4c3b709 is actually unrelated (was missing in #332), but I thought it's ok to sneak these changes in here 😇

[rtroilo]

thank you