Function classifyEnvelope

classifyEnvelope(envelope: GuardEnvelope): OpClass
Assign an operation class to an inbound applet envelope.

kehto treats the class as an opaque key; this is where kernl gives it meaning. Deletions get their own class because a flood of deletes is the cheapest way for an applet to damage an account's public record.
Parameters
- envelope: GuardEnvelope
  The envelope fields the guard classifies on.
Returns OpClass
The operation class the rates and caps are keyed by.
Example
```
classifyEnvelope({ type: 'relay.publish', kind: 5 }); // 'relay:publish:delete'
classifyEnvelope({ type: 'resource.fetch' }); // 'resource:bytes'
classifyEnvelope({ type: 'clipboard.write' }); // 'generic'
```