class Watch

Change notification for power source state using a "hanging-get" pattern.

The first call to this method returns the current hardware state immediately.

Subsequent calls block until a change occurs that matches the provided masks.

At most one `Watch` call may be outstanding at a time per connection.

Completing a call acknowledges that the client has received the previous update.

### Power Management and Suspend

To prevent lost wakeups, the server (driver) must ensure that the `Watch` call

remains active (and hardware interrupts armed) while the system is suspended.

+ **Interest Triggers**: If a change in the `interest` mask occurs while the

system is suspended, the server MUST NOT complete the `Watch` call until

the system wakes for another reason (e.g., a `wake_on` event or external trigger).

This ensures the CPU remains asleep for non-critical updates.

+ **Wake-On Triggers**: If a change in the `wake_on` mask occurs, the server

MUST wake the system and complete the call immediately with a `wake_lease`.

As a result of this queuing behavior, if multiple changes occur while the

system is suspended, they may be merged into a single returned `status` table,

and intermediate state transitions may be lost.

+ `interest`: The client wants to be notified if any of the fields present

in this table change. If any field in `interest` changes, the method returns.

+ `wake_on`: Similar to `interest`, but if a change occurs in these fields,

the server will attempt to keep the system awake using the provided `lease`

(or by returning a `wake_lease`) until the client acknowledges the update.

+ `lease`: A power lease token used to coordinate handoff between the server

and client, ensuring the system does not suspend before the client can

process a critical power event.

Returns:

+ `status`: The updated status table containing the fields that changed.

+ `wake_lease`: An optional lease token provided if the change triggered

a `wake_on` condition and the server is maintaining system state.