Adds back a host/systime for demo only. filter it behind a feature flag

[gbin]

Summary

Related issues

• Closes #

Changes

Testing

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• just lint
• just test
• optional full just std-ci (if std/runtime paths are impacted)
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Checklist

• I have updated docs or examples where needed
• I have added or updated tests where needed
• I have considered platform impact (Linux/macOS/Windows/embedded)
• I have considered config/logging changes (if applicable)
• This change is not a breaking change (or I documented it below)

Breaking changes (if any)

Additional context

[Copilot]

Pull request overview

Adds an optional “host/system perf timing” path so runtime/process timing metadata can reflect wall-clock execution (especially in sims) while keeping message tov on the robot/sim clock.

Changes:

• Introduces cu29::curuntime::perf_now() and a new sysclock-perf feature to switch perf timing to a host clock.
• Updates generated runtime loop + task/bridge execution code to stamp process_time using perf_now().
• Enables the feature in the balancebot + flight-controller simulation examples and updates their message timing helpers.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
examples/cu_rp_balancebot/src/sim_driver.rs	Uses perf_now() for process_time while preserving simulated tov.
examples/cu_rp_balancebot/Cargo.toml	Enables cu29/sysclock-perf for the sim feature set.
examples/cu_flight_controller/src/sim.rs	Updates sim message timing to use perf_now() for process_time.
examples/cu_flight_controller/Cargo.toml	Enables cu29/sysclock-perf in sim_core.
core/cu29_runtime/src/curuntime.rs	Adds perf_now() implementation and docs.
core/cu29_runtime/Cargo.toml	Adds sysclock-perf feature flag.
core/cu29_derive/src/lib.rs	Switches generated perf/process timing stamps from clock.now() to perf_now().
core/cu29/src/lib.rs	Documents the new sysclock-perf feature in crate docs.
core/cu29/Cargo.toml	Wires sysclock-perf feature through the cu29 facade crate.

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