[Backport 2.x] Optimize checksum creation for remote cluster state (#16046)

[himshikha]

Description

Backport for PR #16046

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 1caf05b: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[himshikha]

❌ Gradle check result for 1caf05b: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

Flaky test #14289, #14327, #14314

[github-actions]

❌ Gradle check result for 34eec04: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[himshikha]

❌ Gradle check result for 34eec04: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

Flaky test #15944

[github-actions]

❕ Gradle check result for e93314f: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Attention: Patch coverage is 93.58974% with 5 lines in your changes missing coverage. Please review.

Project coverage is 71.69%. Comparing base (20d32cf) to head (e93314f).
Report is 5 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...pensearch/gateway/remote/ClusterStateChecksum.java	95.45%	3 Missing ⚠️
...arch/gateway/remote/RemoteClusterStateService.java	80.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #16150      +/-   ##
============================================
+ Coverage     71.60%   71.69%   +0.09%     
- Complexity    64716    64786      +70     
============================================
  Files          5278     5278              
  Lines        302835   302870      +35     
  Branches      44059    44059              
============================================
+ Hits         216848   217157     +309     
+ Misses        67932    67599     -333     
- Partials      18055    18114      +59     

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