CNDB-16363: Improve matched rows estimation accuracy for memory indexes

[driftx]

When a memory index contains very few rows and is split into many shards, we can expect a lot of variance in the number of rows between the shards. Hence, if we took only one
shard to estimate the number of matched rows, and
extrapolate that on all shards to compute the estimated matching rows from the whole index, we risk making a huge estimation error.

This commit changes the algorithm to take as many shards as needed to collect enough returned or indexed rows. For very tiny datasets is it's likely to use all shards for estimation. For big datasets, one shard will likely be enough, speeding up estimation.

This change also allows to remove one estimation method. We no longer need to manually choose between the estimation from the first shard and from all shards.

Additionally, the accuracy of estimating of NOT_EQ rows has been improved by letting the planner know the union generated by NOT_EQ is disjoint so the result set cardinality is the sum of cardinalities of the subplans.

The commit contains also a fix for a bug that caused some non-hybrid queries be counted as hybrid by the query metrics.

Unused keyRange parameters have been removed from the methods for estimating row counts in the index classes.

[github-actions]

Checklist before you submit for review

• This PR adheres to the Definition of Done
• Make sure there is a PR in the CNDB project updating the Converged Cassandra version
• Use NoSpamLogger for log lines that may appear frequently in the logs
• Verify test results on Butler
• Test coverage for new/modified code is > 80%
• Proper code formatting
• Proper title for each commit staring with the project-issue number, like CNDB-1234
• Each commit has a meaningful description
• Each commit is not very long and contains related changes
• Renames, moves and reformatting are in distinct commits
• All new files should contain the DataStax copyright header instead of the Apache License one

[driftx]

Adjusted imports. I think this broke SingleRestrictionEstimatedRowCountTest but it wasn't immediately obvious how.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
87.6% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cassci-bot]

❌ Build ds-cassandra-pr-gate/PR-2335 rejected by Butler

---

5 regressions found
See build details here

---

Found 5 new test failures

Test	Explanation	Runs	Upstream
o.a.c.auth.CassandraRoleManagerTest.testPasswordUpdateRateLimitingPerRole (compression)	REGRESSION	🔴	0 / 30
o.a.c.index.sai.cql.EstimatedRowCountTest.testReturnedRowsEstimates[numShards=64, numPartitions=10,000] (compression)	NEW	🔴	0 / 30
o.a.c.index.sai.cql.VectorCompaction100dTest.testPQRefine[dc false] ()	NEW	🔴	0 / 30
o.a.c.index.sai.cql.VectorSiftSmallTest.testSiftSmall[db false] ()	NEW	🔴	0 / 30
o.a.c.index.sai.plan.SingleRestrictionEstimatedRowCountTest.testMemtablesSAI (compression)	REGRESSION	🔴	0 / 30

---

Found 1 known test failures

[djatnieks]

Adjusted imports. I think this broke SingleRestrictionEstimatedRowCountTest but it wasn't immediately obvious how.

We can see if the later commit from CNDB-17275 will help.