[codex] Capture Kompact test logging through libtest

[Bathtor]

Summary

• Add reusable kompact::test_support helpers that route Kompact slog output and the log facade through libtest-captured stdout.
• Allow tests to replace the process default Kompact logger so default KompactConfig systems stay quiet in successful runs.
• Migrate core, network, local example, and network example tests to use captured logging while preserving normal example code paths.

Closes #225.

Validation

The new test-support writer has unit coverage for partial-line buffering and flush behaviour. Existing core component/runtime tests exercise captured logging for default and custom configurations, existing network tests cover reuse from kompact-net, and the local and network example tests cover test initialisation around example entry points.