Single process - Githubissues

The pull request rounds out necessary changes for 3.1.2 including:

Single process mode: If all tasks would run in one process, and a GraphServer/SHMServer combo are already up, ez.run will not attempt multiprocessing. Critical for using ezmsg in REPL/notebook environments.
Associate Publisher and Subscriber objects with OutputStream and InputStream instead of individual tasks:
- Should drastically reduce the number of connections/sockets required for systems, enhancing performance
- Allows for control over individual OutputStream...
  - hostname/port specification; allowing outbound TCP communications to other PCs
  - number of buffers; down to 1 buffer for direct control of channel latency and backpressure
  - initial SHM allocation size; to avoid resizing SHM while running
  - force TCP message passing; for small message sizes, there's no performance loss and this allows us to run perf benchmarks including TCP transmission without multi machine CI setups.
- IMPORTANT BREAKING CHANGE -- it is no-longer possible to subscribe to OutputStreams and publish to InputStreams. This was previously possible (unintended) and should be fixed in downstream projects. If you can come up with a valid use-case, please let me know.
Command line tool that allows for serving/shutting down GraphServer and SHMServer from command line. After installing ezmsg, simply run ezmsg serve from the command line to start up the ezmsg background servers

This pull request also:

Fixes several small bugs
Switches SHMServer and GraphServer ports (25978/9). GraphServer now sits at 25978 by default, and SHMServer now sits at 25979 by default.
- Incidentially, this was driven by trying to run the servers through SSH forwarding on a remote machine. I learned we should NEVER forward the SHMServer port (oops; seems pretty obvious to me now). Figured we should set the GraphServer to the base port -> 25978 represented as a 16-bit unsigned number in binary is 0110010101111010, which when represented by two ascii characters is the string ez 👍
SHMServer, GraphServer and the publisher port-range start are now individually configurable by environment variables.
GraphServer's pause and resume are no-longer asynchronous; don't need to be await'ed
Shuts down immediately after NormalTermination is raised, rather than waiting up to 0.5 seconds
- Tests run ever-so-slightly-faster because of this

ezmsg-org / ezmsg