NfbPlugin: log warning instead of exiting on NUMA node detection failure

[SiskaPavel]

Summary

Log a warning instead of returning an error when NUMA node detection fails.

Details

Previously, failing to detect a NUMA node caused the function to return an error and abort execution.
Now, the code prints a warning to stderr and continues running, allowing the program to operate without NUMA preference.

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✅ Checks

• Relevant documentation was updated (if needed)
• CI pipeline passes (build, tests, lint, static analysis)
• New code follows clang-tidy rules
• The change is clearly related to a specific issue / requirement
• Documentation (e.g. Doxygen) is updated if needed
• The PR is rebased on the latest master
• No unrelated changes are included

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