chore: small fixes for simulation subprocess tracking

[not-matthias]

No description provided.

[greptile-apps]

Greptile Summary

This PR makes subprocess tracking a presence-only CLI flag and ties both Valgrind instrumentation startup and thread separation to that setting.

• Allows --simulation-track-subprocess without a value.
• Enables inherited instrumentation and per-thread Callgrind output only while subprocess tracking is enabled.
• Leaves cycle estimation responsible only for --cycle-estimation=yes.

Confidence Score: 5/5

The PR appears safe to merge based on the accepted review findings, with the explicitly acknowledged experimental Tracegrind limitation remaining a deliberate follow-up decision.

No unacknowledged, concretely reachable failure was established in the changed CLI parsing or Callgrind output behavior.

Important Files Changed

Filename	Overview
src/cli/shared.rs	Simplifies subprocess-tracking argument parsing to support the bare boolean flag; no actionable current compatibility failure was established.
src/executor/valgrind/measure.rs	Rebinds thread separation to subprocess tracking; the known Tracegrind incompatibility is explicitly acknowledged in the PR description.

_{Reviews (1): Last reviewed commit: "refactor(valgrind): tie --separate-threa..." | Re-trigger Greptile}

[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.

✅ 17 untouched benchmarks

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_{Comparing chore/small-fixes (ab1a9fb) with main (e5587f4)}