recursive serialization fails with nested objects

When serializing nested more than 511 dictionaries deep, `msgpack`, used by `distributed.protocol.core.dumps` hits a hard coded recurrsion limit.

```
distributed.protocol.core - CRITICAL - Failed to Serialize
Traceback (most recent call last):
File "/Users/kgerman/anaconda3/envs/daskdev/lib/python3.9/site-packages/distributed/protocol/core.py", line 76, in dumps
frames[0] = msgpack.dumps(msg, default=_encode_default, use_bin_type=True)
File "/Users/kgerman/anaconda3/envs/daskdev/lib/python3.9/site-packages/msgpack/__init__.py", line 35, in packb
return Packer(**kwargs).pack(o)
File "msgpack/_packer.pyx", line 294, in msgpack._cmsgpack.Packer.pack
File "msgpack/_packer.pyx", line 300, in msgpack._cmsgpack.Packer.pack
File "msgpack/_packer.pyx", line 297, in msgpack._cmsgpack.Packer.pack
File "msgpack/_packer.pyx", line 231, in msgpack._cmsgpack.Packer._pack
File "msgpack/_packer.pyx", line 231, in msgpack._cmsgpack.Packer._pack
File "msgpack/_packer.pyx", line 231, in msgpack._cmsgpack.Packer._pack
[Previous line repeated 508 more times]
File "msgpack/_packer.pyx", line 229, in msgpack._cmsgpack.Packer._pack
File "msgpack/_packer.pyx", line 163, in msgpack._cmsgpack.Packer._pack
ValueError: recursion limit exceeded.
```