Explain API changes

[neetikasinghal]

Description

Explain API high level changes for the POC.

Related Issues

Resolves #875

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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.

[Vikasht34]

We need to have Unit test for each case

1. Disk-based search with valid rescore context.
2. Radial search.
3. ANN search (default case).
4. Shard-level rescoring enabled.
5. Shard-level rescoring disabled.
6. Filter weight case where filtered IDs are less than k.
7. Filter threshold value greater than cardinality.
8. Missing native engine files.
9. Valid context with matching document and disk-based search.

And Please validate with Explaination Object.

[Vikasht34]

Could we improve readability of this function , I see this function is doing

1. Building Score
2. Build the main explanation
3. Build the detailed explanation for the leaf node.

Would we start with something simple

public Explanation explain(LeafReaderContext context, int doc) {
   //Function to Calculate Score
    // Build the main explanation

      // Build the detailed explanation for the leaf node
    return Explanation.match(score, mainExplanation, Explanation.match(score, leafExplanation));
}

And Please break down other functions as well when needed.

[neetikasinghal]

sure i will refactor this.

[neetikasinghal]

We need to have Unit test for each case

1. Disk-based search with valid rescore context.
2. Radial search.
3. ANN search (default case).
4. Shard-level rescoring enabled.
5. Shard-level rescoring disabled.
6. Filter weight case where filtered IDs are less than k.
7. Filter threshold value greater than cardinality.
8. Missing native engine files.
9. Valid context with matching document and disk-based search.

And Please validate with Explaination Object.

@Vikasht34 yes the tests are not yet added in here, hence its in a draft status. I will add the coverage with all the possible cases.