Validate chassis path before populating FanZone Chassis link

Update asyncPopulatePid to verify that the chassis name extracted from the PID zone configuration path exists in the inventory. Instead of unconditionally setting the Chassis link, the code now queries the inventory subtree paths and only populates the Chassis link if a matching chassis is found. Unit tests have been added to verify behavior for both valid and invalid chassis configurations.

Google-Bug-Id:545645561
PiperOrigin-RevId: 967474295
Change-Id: I9af3608887d53435f2509879ed6510ed0974917c