tracing: add hpx::tracing::rename_region abstraction

[v4xsh]

Proposed Changes

• Add hpx::tracing::rename_region free function to the unified tracing abstraction layer in libs/core/tracing
• Implement Tracy backend by delegating to hpx::tracy::detail::rename_region; ITT and no-op branches are inline no-ops in the header since ITTNotify has no rename equivalent
• Replace the raw #if defined(HPX_HAVE_MODULE_TRACY) / tracy::detail::rename_region / #endif block in thread_data.cpp with a clean backend-agnostic hpx::tracing::rename_region(...) call

Any background context you want to provide?

Checklist

• I have added a new feature and have added tests to go along with it.
• I have fixed a bug and have added a regression test.
• I have added a test using random numbers; I have made sure it uses a seed, and that random numbers generated are valid inputs for the tests.

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[codacy-production]

Up to standards ✅

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[hkaiser]

LGTM, thanks!