CNDB-18137 fix linter warnings in files effected by CNDB-15608

[k-rus]

Fixes https://github.com/riptano/cndb/issues/18137

Fixes IntelliJ linter warnings in files affected during work on
CNDB-15608 to reduce warning noise:

• Fix single character strings to character constants
• Remove unused imports
• Remove unnecessary throw in method declarations
• Simplify assert in a test
• Remove undocumented fields from javadoc
• Remove unnecessary resource suppression
• Simplify string join
• Remove unused logger field
• Remove unnecessary curly braces in lambda expression
• Remove unnecessary cast

[github-actions]

Checklist before you submit for review

• This PR adheres to the Definition of Done
• Make sure there is a PR and ticket 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 IBM copyright header instead of the Apache License one (no DataStax copyright any longer)

[plpesvc-ds]

❌ Build ds-cassandra-pr-gate/PR-2453 rejected by Butler

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2 regressions found
See build details here

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Found 2 new test failures

Test	Explanation	Runs	Upstream
o.a.c.index.sai.cql.VectorCompaction100dTest.testZeroOrOneToManyCompaction[version=ec enableNVQ=false]	REGRESSION	🔴⚪	0 / 30
o.a.c.index.sai.cql.VectorSiftSmallTest.testSiftSmall[ed false]	REGRESSION	🔴🔴	0 / 30

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Found 5 known test failures

[michaelsembwever]

please make sure (/check) these changes (outside of sai) align with upstream.

fixing lint issues is trivial and can cause a lot of unnecessary headache on rebases.

it is better to start with fixing code style upstream first and wait for it to come back to us, then bear the rebase costs. this obviously does not apply to the sai code.