ci: fix SHM checks

[avinxshKD]

Fixes two SHM CI issues

• add the repo root include path for the C++ SHM smoke compile
• make the SHM concurrency reader time-bounded instead of waiting for every writer update

The old reader assumption was too strict for polling shared memory and could time out on CI

[avinxshKD]

@pradeeban CI is green now :p