[broadcast] Fix issues with gateway merge to main

[parasj]

On main, there are various PyType errors. Many are imports to old copies of the gateway but there are still some errors in gateway_daemon_api.py.

$ black -l 140 . && pytype . --config .pytype.cfg -j 16                                                                                                                                                                                                                                                                                
All done! ✨ 🍰 ✨
99 files left unchanged.
Computing dependencies
Analyzing 85 sources with 3 local dependencies
ninja: Entering directory `.pytype'
[1/3] check skyplane.broadcast.gateway.gateway_daemon_api
FAILED: /Users/paras/code/skylark/.pytype/pyi/skyplane/broadcast/gateway/gateway_daemon_api.pyi 
/opt/homebrew/Caskroom/miniconda/base/bin/python -m pytype.single --imports_info /Users/paras/code/skylark/.pytype/imports/skyplane.broadcast.gateway.gateway_daemon_api.imports --module-name skyplane.broadcast.gateway.gateway_daemon_api --platform darwin -V 3.10 -o /Users/paras/code/skylark/.pytype/pyi/skyplane/broadcast/gateway/gateway_daemon_api.pyi --analyze-annotated --nofail --quick /Users/paras/code/skylark/skyplane/broadcast/gateway/gateway_daemon_api.py
File "/Users/paras/code/skylark/skyplane/broadcast/gateway/gateway_daemon_api.py", line 40, in GatewayDaemonAPI: Name 'Optional' is not defined [name-error]
File "/Users/paras/code/skylark/skyplane/broadcast/gateway/gateway_daemon_api.py", line 191, in make_chunk_req_payload: No attribute 'name' on str [attribute-error]
  In Union[Any, str]
File "/Users/paras/code/skylark/skyplane/broadcast/gateway/gateway_daemon_api.py", line 198, in get_chunk_reqs: No attribute 'chunk' on int [attribute-error]
  In Union[Any, int]
File "/Users/paras/code/skylark/skyplane/broadcast/gateway/gateway_daemon_api.py", line 306, in get_receiver_compression_profile: No attribute 'get_chunk_request' on skyplane.broadcast.gateway.chunk_store.ChunkStore [attribute-error]

For more details, see https://google.github.io/pytype/errors.html
[2/3] check skyplane.broadcast.gateway.operators.gateway_operator
ninja: build stopped: subcommand failed.
Leaving directory '.pytype'

@sarahwooders can you adopt this PR and look into the remaining errors?

[sarahwooders]

Yeah will do!