Native stack overflow in SimDrive::set_ach_speed: unbounded self-recursion on infeasible steps

sd.walk() can kill the host process with a native stack overflow (Windows exit 0xC00000FD, SIGSEGV on Linux) with no Python exception raised. I was able to trace the stack overflow to set_ach_speed, which recurses on itself (fastsim-core/src/simdrive/mod.rs:735) with no depth cap, and its only exit is the cyc_met check, a hard pwr_tractive <= pwr_prop_fwd_max with no tolerance. We could add a recursion/iteration cap on the correction (mirroring ach_speed_max_iter), or perhaps revise the criteria for stopping the recursion.

Reproduce:

import fastsim as fs
veh = fs.Vehicle.from_file("vehicles/2016 TOYOTA Corolla 4cyl 2WD.yaml")
veh.set_save_interval(1)
cyc = fs.Cycle.from_file("cycles/<any trip id from manifest>.yaml")
fs.SimDrive(veh, cyc).walk()  # process dies natively

set_ach_speed

Start by reproducing the native crash with the provided Python example, then inspect set_ach_speed in fastsim-core/src/simdrive/mod.rs around the linked location and the reported recursion site. Trace the cyc_met stopping condition and compare the correction logic with ach_speed_max_iter. Done means infeasible steps no longer exhaust the native stack and the simulation exits or reports failure safely.