Add const-correctness to read-only APIs across state, control, network, and sync modules

[Copilot]

This addresses missing const qualifiers on functions and values that are semantically read-only, with emphasis on getters and pure decision helpers. The update improves const-correctness without changing behavior.

• Elevator state + node getters

  • Marked read-only ElevatorState accessors as const (Id, Floor, Active, Obstruction, Fault, DoorOpen, Stopped, MotorDir, MovingState, Version, Requests, Inertia, Usable).
  • Marked ElevatorNode::Id() and ElevatorNode::Running() as const.
  • Updated CopyFrom/OnUpdate signatures to use const-safe parameters (const ElevatorState*, const ElevatorState&).

• Control/request table decision surface

  • Marked RequestTable readers as const (Value, Table, IsRequestAbove/Below/Here).
  • Marked read-only controller methods as const (Requests, ShouldStop, ShouldClearImmediately, ChooseDirection, ClearCurrentFloor).

• Order sync + packet accessors

  • Marked Order getters as const; made ObservedBy and OnUpdate const-correct.
  • Added const overload for OrderTable::Order(...) and made ToBoolTable/Join const-correct.
  • Marked NetworkPacket::Id() as const and added const overloads for Orders(), State(), CabButtonOrders().

• Peers read-only methods + local const usage

  • Marked Peers::ObservedByAll, CalculateElevatorCosts, and NumElevs as const.
  • Tightened call-site locals to const where values are not mutated (e.g., selected booleans and copied orders).

// Before
int ElevatorState::Id();
void Order::OnUpdate(Order rcv);
ordersync::Order* OrderTable::Order(int floor, int btn);

// After
int ElevatorState::Id() const;
void Order::OnUpdate(const Order& rcv);
const ordersync::Order* OrderTable::Order(int floor, int btn) const;

• Fixes fix: add const to functions #5

[eskfro]

Looks fine.