Granular frame scheduling and error types - #1869

This is an experimental PR to port some of the Ziggurat frame scheduling improvements back to zigpy. bellows and zigpy-ziggurat are the current test targets but the other radio libraries will be migrated once the API stabilizes so the compatibility shim in this PR can be removed.

• Radio libraries now implement _send_packet, not send_packet, and remove all concurrency and rate limiting. It's a simple interface to send a single packet. Nothing more.
• Rate limiting is done dynamically based on radio backpressure indicators and takes into account both concurrency and total bytes used by each request.
• There are now granular zigpy error codes for enqueuing errors (packet is too long, no space in buffers, firmware concurrency limit is exhausted, etc.) and delivery errors (CCA, broadcast storm, no ACK, no route, etc.).
• Sends go through multiple stages: queued (we want to send and are waiting for a slot), parked (we are waiting for a sleepy end device to wake up), in-flight (we sent the packet and are waiting for a transmission confirmation), awaiting reply, and done. Before, we encoded this entire delivery mechanism within Python stack frame locals. Now, we know exactly what is being sent, queued, etc. Good for a future debug UI.
• Requests to sleeping end devices can be parked and will wait until the device is awake. This benefits from the granular request state tracking because we can tell where a request timed out: we can still attach a 60s delivery timeout to a request that waits 1 hour for a device to wake up.
• coalesce_key allows requests to supersede one another. This allows multiple queued up requests that control the same device state (i.e. bulb color or switch state) to replace one another, allowing them to effectively occupy the same send slot when waiting for the radio to free up. We can further improve this rate limit groupcasts better.

Radio library branches:

• https://github.com/puddly/bellows/tree/puddly/zigpy-scheduling-api
• https://github.com/zigpy/zigpy-ziggurat/tree/puddly/zigpy-scheduling-api

This PR + one of those is enough to test this PR out.