refactor predictable: add method to check if model is ready

[ylwu-amzn]

Description

[Describe what this change achieves]

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

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[codecov]

Codecov Report

Merging #1057 (c30752a) into 2.x (e2c9948) will increase coverage by 0.13%.
The diff coverage is 41.02%.

@@             Coverage Diff              @@
##                2.x    #1057      +/-   ##
============================================
+ Coverage     78.40%   78.54%   +0.13%     
- Complexity     1928     1944      +16     
============================================
  Files           157      157              
  Lines          7934     7960      +26     
  Branches        796      797       +1     
============================================
+ Hits           6221     6252      +31     
+ Misses         1357     1353       -4     
+ Partials        356      355       -1     

Flag	Coverage Δ
ml-commons	78.54% <41.02%> (+0.13%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...a/org/opensearch/ml/engine/algorithms/DLModel.java	82.69% <0.00%> (-1.63%)	⬇️
...l/engine/algorithms/ad/AnomalyDetectionLibSVM.java	85.71% <0.00%> (-1.13%)	⬇️
...search/ml/engine/algorithms/clustering/KMeans.java	90.47% <0.00%> (-1.46%)	⬇️
.../ml/engine/algorithms/clustering/RCFSummarize.java	82.02% <0.00%> (-0.94%)	⬇️
...ml/engine/algorithms/rcf/BatchRandomCutForest.java	88.00% <0.00%> (-1.19%)	⬇️
...ine/algorithms/rcf/FixedInTimeRandomCutForest.java	84.61% <0.00%> (-0.83%)	⬇️
...engine/algorithms/regression/LinearRegression.java	90.90% <0.00%> (-0.93%)	⬇️
...gine/algorithms/regression/LogisticRegression.java	79.06% <0.00%> (-0.94%)	⬇️
...search/ml/engine/algorithms/sample/SampleAlgo.java	80.00% <0.00%> (-3.34%)	⬇️
...va/org/opensearch/ml/task/MLPredictTaskRunner.java	80.82% <12.50%> (-1.58%)	⬇️
... and 1 more

... and 4 files with indirect coverage changes