Mpservice

- `mpservice.util.ProcessLogger` gets context manager methods.
- New class `mpservice.util.SpawnProcess`.

- Add dependency `asgiref`.
Previously we've relied on getting `asgiref` from `uvicorn` dependency,
which is a bad idea. Recently, `uvicorn` removed its dependency on `asgiref`.
- Reduce the default frequency of resource utilization logs.

- Refinement and simplification to `streamer`.
- Refinement to `server_process`.

- Added `mpservice.mpserver.ThreadWorker` and `ThreadServlet`.
- Simplified `mpserver` parameter for CPU pinning spec.
- Added log on worker process CPU/memory utilization in `mpserver`.

- Refactor to `mpserver` with API changes.
New design allows flexible composition of sequential and ensemble setups,
leading to considerable enhancements in capability and flexibility.
There are also considerable improvements to the implementation
(in terms of simplicity, elegance, robustness).
- Replaced all uses of `time.monotonic` by `time.perf_counter`, which has much
higher resolution.
- Added module `named_pipe`.

- Added (or brought back) parameter `backlog` to `MPServer`.
- Implimentation improvements: simplified utitlity queues; removed error pipe of MPServer.