server/storage: simplify CreateConfigChangeEnts and GetEffectiveNodeIDsFromWALEntries

[callthingsoff]

By using maps and slices functions.

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @callthingsoff. Thanks for your PR.

I'm waiting for a etcd-io member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.98%. Comparing base (14cf669) to head (f785fb6).

Additional details and impacted files

Files with missing lines	Coverage Δ
server/storage/util.go	80.00% <100.00%> (-1.58%)	⬇️

... and 22 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19419      +/-   ##
==========================================
+ Coverage   68.95%   68.98%   +0.02%     
==========================================
  Files         420      420              
  Lines       35753    35747       -6     
==========================================
+ Hits        24655    24659       +4     
+ Misses       9677     9667      -10     
  Partials     1421     1421              

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