fix(valgrind): install libc6-dbg during valgrind setup

[not-matthias]

This takes around 10 seconds, so it shouldn't be an issue that it's not cached + prevents complexities of cache invalidation

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 7 untouched benchmarks

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_{Comparing cod-2770-unresolved-symbol-in-exec-cli-simulation-benchmarks (23e64a3) with main (7e86f11)}

[greptile-apps]

Greptile Summary

This PR installs libc6-dbg (glibc debug symbols) alongside the CodSpeed valgrind binary during the valgrind setup step, fixing crashes on GitHub-hosted runners that ship without those symbols by default.

• is_valgrind_installed() is extended to require both valgrind (via get_valgrind_status) and libc6-dbg (via the new apt::is_package_installed helper), so a stale cache entry that only contains valgrind will no longer be treated as a complete installation.
• libc6-dbg is added to the same apt::install call as the valgrind .deb and to the returned package-names vector, ensuring it is cached and subject to the same idempotency logic as valgrind itself.

Confidence Score: 5/5

The change is safe to merge; it correctly fixes the missing libc6-dbg on GitHub runners and properly threads it through both the install and cache layers.

Both the installation path and the idempotency guard (is_valgrind_installed) are updated consistently. Stale caches that contain valgrind but not libc6-dbg will correctly fall through to a full reinstall because is_package_installed returns false. The issues flagged in previous review threads have all been addressed in this revision.

No files require special attention.

Important Files Changed

Filename	Overview
src/executor/helpers/apt.rs	Adds is_package_installed helper that shells out to dpkg -s and checks the exit code correctly.
src/executor/valgrind/setup.rs	Updates is_valgrind_installed to require libc6-dbg presence, and co-installs and co-caches it with valgrind, correctly handling stale-cache and fresh-install scenarios.

Sequence Diagram

sequenceDiagram
    participant CI as CI Runner
    participant IC as install_cached
    participant IV as is_valgrind_installed
    participant DS as dpkg -s libc6-dbg
    participant APT as apt::install
    participant Cache as Cache Dir

    CI->>IC: install_valgrind(system_info, cache_dir)
    IC->>IV: is_valgrind_installed()
    IV->>IV: get_valgrind_status()
    IV->>DS: dpkg -s libc6-dbg
    DS-->>IV: exit 0/1
    IV-->>IC: true / false

    alt Both valgrind and libc6-dbg present
        IC-->>CI: Ok(()) skip install
    else Stale cache missing libc6-dbg
        IC->>Cache: restore_from_cache()
        IC->>IV: is_valgrind_installed() again
        IV->>DS: dpkg -s libc6-dbg
        DS-->>IV: exit 1
        IV-->>IC: false fall through
        IC->>APT: install valgrind.deb libc6-dbg
        APT-->>IC: Ok(())
        IC->>Cache: save_to_cache valgrind libc6-dbg
    else Fresh install
        IC->>APT: install valgrind.deb libc6-dbg
        APT-->>IC: Ok(())
        IC->>Cache: save_to_cache valgrind libc6-dbg
    end
    IC-->>CI: Ok(())

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