"Really Efficient" mode

[jennydaman]

This PR introduces a mechanism for calling px-repack once at the end of the series, instead of for each DICOM file. As a result, performance is greatly improved.

Design Overview

pypx/README.rst

Lines 267 to 296 in a6ebedb

	6. "Really Efficient" Mode
	**************************
	Really Efficient using px-REcount to call px-REpack with the help of REdis.
	Typically, a `px-repack` process is called per received DICOM file.
	``px-find --reallyEfficient --then receive`` does one `px-repack`
	per series (i.e. one directory of DICOM files). This dramatically
	improves performance See benchmarks_.
	"Really efficient" (RE) mode requires a redis server.
	In RE mode, ``px-find`` records the number of DICOM files per series (``NumberOfSeriesRelatedInstances``) to redis.
	``storescp`` is configured to run ``px-recount`` on each instance instead of ``px-repack``.
	``px-recount`` does nothing until the entire series is received.
	Finally, ``px-recount`` calls ``px-repack`` once on the entire series.
	``px-recount`` is implemented in Rust to reduce its footprint when being
	called once per instance.
	RE Mode Usage
	=============
	To use RE mode, install ``pypx`` in RE mode (``pip install 'pypx[re]'``)
	and run ``storescp`` as
	.. code-block:: bash
	storescp --fork -od /tmp/data -pm -sp -xcr 'px-recount --xcrdir \"#p\" --xcrfile \"#f\" --verbosity 0 --logdir /home/dicom/log --datadir /home/dicom/data --cleanup' 11113

A Rust project, px-recount, is added to this repo. Its functionality is described here:

pypx/px-recount/src/main.rs

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	px-recount has the same command-line options as px-repack.
	Its intended usage is as a DICOM instance handler called by storescp:
	storescp --fork -od /tmp/data -pm -sp -xcr 'px-recount --xcrdir \"#p\" --xcrfile \"#f\" --verbosity 0 --logdir /home/dicom/log --datadir /home/dicom/data --cleanup' 11113
	px-recount runs px-repack if the received DICOM file given by --xcrdir
	and --xcrfile is the last of its series. The number of files of a
	series received so far are counted by px-repack and saved to a Redis
	database.
	The algorithm:
	0. On input of a DICOM file
	1. Read DICOM tags to get SeriesInstanceUID
	2. Get NumberOfSeriesRelatedInstances and fileCounter from Redis
	3. If this file is the last of its series, run px-repack.
	Else, write fileCounter+1 to Redis.
	ENVIRONMENT VARIABLES
	PYPX_REDIS_URL Redis connection URL (example: redis://redis-server.svc.local:6379)
	NOTES
	- It is expected that px-find writes NumberOfSeriesRelatedInstances for
	the series before px-recount runs. This is typically achieved by running
	px-find --reallyEfficient --then receive ...
	- Generally, px-recount is fail-safe. It will call px-repack in the event
	of any redis-related exceptions.