refactor memory layer APIs

[Zhangxunmt]

Description

Refactor Memory APIs to resolve #1875

Verified all refactored APIs listed in the above issue run fine in my dev desk.

Issues Resolved

[List any issues this PR will resolve]

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (38b51f2) 82.63% compared to head (a3f1d62) 82.61%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1877      +/-   ##
============================================
- Coverage     82.63%   82.61%   -0.02%     
+ Complexity     5391     5387       -4     
============================================
  Files           521      521              
  Lines         21724    21705      -19     
  Branches       2211     2209       -2     
============================================
- Hits          17952    17932      -20     
- Misses         2873     2876       +3     
+ Partials        899      897       -2     

Flag	Coverage Δ
ml-commons	82.61% <100.00%> (-0.02%)	⬇️

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[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-1877-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 b3c033fd171eb5beb02cf6458d3e498a50b70174
# Push it to GitHub
git push --set-upstream origin backport/backport-1877-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-1877-to-2.x.