aajoshi/improve intermediate calc stage

[ashiijo]

Issues

• My PR addresses the following Helix issues and references them in the PR description:

This PR is for improvement for IntermediateStateCalculationStage
These improvements are made on basis of profiling data acquired -
https://observe.prod.linkedin.com/profiling-explorer/event/2963846

Description

Improvements made -

1. Remove unnecessary HashSet initialisation

modified to remove expensive HashSet init, which allocates separate memory and copies all data to the new set

2. Cache per partition calculations for Partition comparator instead of re-calculating for every run

3. Improve deepcopy during partition comparator init, remove unnecessary use of streams which adds overhead

4. Remove unnecessary anymatch operation which creates stream and causes overhead, also remove .contains() use, and rely on equals

Tests

NA

Changes that Break Backward Compatibility (Optional)

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(Consider including all behavior changes for public methods or API. Also include these changes in merge description so that other developers are aware of these changes. This allows them to make relevant code changes in feature branches accounting for the new method/API behavior.)

Documentation (Optional)

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Commits

• My commits all reference appropriate Apache Helix GitHub issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Code Quality

• My diff has been formatted using helix-style.xml
  (helix-style-intellij.xml if IntelliJ IDE is used)

[ngngwr]

LGTM