Worker: report Hardware to the control plane during worker registration #2247

When a worker comes up, it currently only reports its compute and actor capacity to the control plane. To support hardware-aware snapshot scheduling and restore, each worker should also report its hardware identity (starting with CPU architecture) as part of registration so capacity and hardware are recorded together on the worker's status before the worker becomes eligible for scheduling.

Proposal

Update WorkerService so atelet reports the worker's HardwareIdentity alongside its Capacity in a single atomic update (replacing SetWorkerCapacity with RegisterWorker, or adding HardwareIdentity hardware to the existing RPC):
(this is just a draft proto)

service WorkerService {
  // Register records a Worker's capacity and hardware compatibility.
  // Idempotent: re-sending the same value is not a write.
  rpc Register(RegisterRequest) returns (RegisterResponse);
}
message RegisterRequest {
  // +k8s:required
  // +k8s:subfield(atespace)=+k8s:forbidden
  ObjectRef worker = 1;
  // +k8s:required
  WorkerResources capacity = 2;
  // +k8s:required
  Hardware hardware = 3;
}
message RegisterResponse {
  Worker worker = 1;
}
message WorkerStatus {
  // ... state, capacity, allocated, observed_epoch ...
  // +k8s:optional
  Hardware hardware = 5;
}

Hardware identity should be reported by each worker (ateom) and relayed through atelet to the control plane, rather than probed once per node by atelet. This ensures that once runtime-specific CPU feature masking or multiple sandbox runtime versions per worker are introduced, the reported hardware identity reflects what the guest sandbox actually sees.