Return a more precise message when throttles have been exceeded.

### Problem

Currently, when a throttle was been exceeded, the node returns a `BUSY` message. The message can be made more useful if the returned message was more specific on which throttle was breached.

### Solution

Instead of returning a boolean value that indicates whether a throttle has been exceeded, return an enum to indicate which throttle was breached. This way a more informative status message can be returned to the caller.

### Alternatives

_No response_