CNDB-15999: Add Directories.getCFDirectoriesUnchecked() to avoid remote I/O blocking

[driftx]

What is the issue

Fixes #15999

What does this PR fix and why was it fixed

Provides a method to get CF directories without checking if they are directories

[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

[eolivelli]

We usually add a comment to say that this method is used by CNDB and it is not to be removed.

Is it possible to add unit tests ? It may seem weird to add unit tests for such small changes but at least we don't lower our global score

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cassci-bot]

❌ Build ds-cassandra-pr-gate/PR-2123 rejected by Butler

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3 regressions found
See build details here

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Found 3 new test failures

Test	Explanation	Runs	Upstream
junit.framework.TestSuite.org.apache.cassandra.distributed.test.CASMultiDCTest-_jdk11	REGRESSION	🔴🔵	0 / 17
paxos_test.TestPaxos.test_contention_many_threads (offheap-bti)	REGRESSION	🔴🔵	0 / 17
o.a.c.cql3.validation.operations.AggregationQueriesTest.testAggregationQueryShouldNotTimeoutWhenItExceedesReadTimeout (compression)	REGRESSION	🔴🔴	2 / 17

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Found 4 known test failures

[eolivelli]

LGTM