KAFKA-12464: enhance constrained sticky Assign algorithm (#10509)

1. Make code simpler and cleaner
2. After the PR: the testLargeAssignmentAndGroupWithUniformSubscription (1 million partitions) will run from ~2600 ms down to ~1400 ms, improves 46% of performance, almost 2x faster!!

Reviewers: Anna Sophie Blee-Goldman <[email protected]>, Guozhang Wang <[email protected]>

Author: showuon