* master:
  go/zodb: Loader: Document that loaded buffer must not be modified
  go/zodb: Split Loader & co. interfaces from IStorage
  go/zodb: Document that Tid(0) is invalid while Oid(0) is valid.
  fixup! go/zodb: Tweak documentation a bit so it renders more well in godoc

The reason for this is that the buffer can be shared with other loaders
via cache.

There are situations when we want to work with, or emulate, only subset
of whole IStorage functionality, with one already established example
being Cache. For this reason split IStorage interface into finer-grained
ones. For now:

	- Loader
	- Prefetcher
	- Iterator
	- Committer
	- Notifier

Oid(0) represents root database object. We cannot change this.

Missed few places in 8685b742.

* master: (29 commits)
  go/zodb: Tweak documentation a bit so it renders more well in godoc
  go/neo/t/nxd/runTestSuite: Also run go & py unit tests in addition to bench-local
  go/neo/t/nxd/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
  go/neo/t/nxd/runTestSuite: New wrapper to run neotest as part of Nexedi testing infrastructure
  go/neo/t/benchplot: New program to visualise neotest benchmarks (draft)
  go/neo/t/neotest: Add bench-local and bench-cluster commands
  go/internal/xzlib: Switch to github.com/DataDog/czlib to zlib Decompression
  go/internal/xzlib: Try to reuse zlib decoders
  go/neo/t/neotest: bench-cpu += unzlib for wczblk1 and prod1 objects
  go/neo/t/neotest: Switch to zwrk to simulate parallel load from multiple clients
  go/zodb: Allow to open a storage in "direct" mode - without local cache
  go/neo/t/neotest: ZODB benchmarks
  go/neo/t/neotest: Network information & benchmarks
  go/neo/t/neotest: Disk information & benchmarks
  go/neo/t/neotest: CPU information & benchmarks
  go/neo/t: Neotest start
  go/zodb/zeo: Add support for protocols preceding ZEO5
  go/zodb: Teach ZODB/go to access ZEO (draft)
  go/zodb: Start putting pickle-related utilities into internal/pickletools package
  go/neo/neonet: Lightweight mode
  ...

While at it add draft overview of data model & friends to package
documentation.

We send output from tested process to master. We also print it to
stdout,stderr so it appears in testnode logs.

However till now it was like, whole output first read, and only then
emitted to log as a whole, thus not allowing to oversee current test
progress by watching testnode log tail.

Fix it by implementing the teeing process manually.

Some draft history related to this patch:

	lab.nexedi.com/kirr/neo/commit/aa370ca3        fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
	lab.nexedi.com/kirr/neo/commit/096550b1        fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
	lab.nexedi.com/kirr/neo/commit/63956f43        fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
	lab.nexedi.com/kirr/neo/commit/b9819d0e        X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally

The wrapper runs `neotest bench-local` in neotest SlapOS instance:

	https://lab.nexedi.com/nexedi/slapos/blob/ab8705f4/software/neotest/instance.cfg.in

Extracted from nexedi/slapos!282

Add the program that reads results from either bench-local or bench-cluster
neotest output and visualizes it. It uses benchlib.py module to read data
in Go benchmark format(*), processes them and plots scalability and other
graphs via matplotlib.

There are lots of hacks and rough edges, and in particular callout coordinate
calculation is completely wrong. However even in this state benchplot was used
to prepare the graphs in http://navytux.spb.ru/~kirr/neo.html and
http://navytux.spb.ru/~kirr/misc/neo·P4.html .

Some draft history related to this patch:

	lab.nexedi.com/kirr/neo/commit/078c9ac3        X move benchlib to -> https://lab.nexedi.com/kirr/pygolang
	lab.nexedi.com/kirr/neo/commit/0edd5129        X benchplot: Teach it to understand benchmark names for partitioned NEO clusters
	lab.nexedi.com/kirr/neo/commit/a1dde3c9        X deco-rio timings
	lab.nexedi.com/kirr/neo/commit/916782b6        X normalize/convert units, so that disk and ping/tcp latencies could be plotted too
	lab.nexedi.com/kirr/neo/commit/f5fec740        X switch node info to labels; start adding that to plot
	lab.nexedi.com/kirr/neo/commit/906462a3        X neotest: Move cluster / node out fro benchmark name to label in environment
	lab.nexedi.com/kirr/neo/commit/cceca65f        X benchplot: Start of automated plotting for neotest benchmark data
	lab.nexedi.com/kirr/neo/commit/a9b10a45        X benchlib/benchstat: Emit label:value info for several labels on one line, similary to go version
	lab.nexedi.com/kirr/neo/commit/502d9477        X benchlib: Python module to read & work with data in Go benchmark format

(*) benchlib.py is now part of pygolang: https://pypi.org/project/pygolang .

These commands do full benchmarking for localhost and networked cases:

- show system info
- do server & client cpu benchmarks
- do server disk benchmarks
- for networked case: do network benchmarks
- tail to either zbench-local or zbench-cluster

It was full `neotest bench-local` that was used to prepare benchmarks
for http://navytux.spb.ru/~kirr/neo.html and http://navytux.spb.ru/~kirr/misc/neo·P4.html

name                 old time/op    new time/op    delta
unzlib/py/wczdata      20.8µs ± 2%    20.7µs ± 1%     ~     (p=0.421 n=5+5)
unzlib/go/wczdata      64.4µs ± 1%    21.3µs ± 0%  -66.89%  (p=0.008 n=5+5)
unzlib/py/prod1-avg    4.00µs ± 1%    4.02µs ± 1%     ~     (p=0.421 n=5+5)
unzlib/go/prod1-avg    10.4µs ± 1%     4.3µs ± 1%  -58.72%  (p=0.008 n=5+5)

There is also unsafe interface with czlib.UnsafeDecompress & friends which I
had not tried because even using safe interface brings ~ 3x speedup.

name                 old time/op    new time/op    delta
unzlib/py/wczdata      20.7µs ± 2%    20.8µs ± 2%     ~     (p=0.548 n=5+5)
unzlib/go/wczdata      70.6µs ± 0%    64.4µs ± 1%   -8.85%  (p=0.008 n=5+5)
unzlib/py/prod1-avg    4.02µs ± 1%    4.00µs ± 1%     ~     (p=0.167 n=5+5)
unzlib/go/prod1-avg    15.2µs ± 0%    10.4µs ± 1%  -31.59%  (p=0.008 n=5+5)

still on wczdata and prod1 much slower compared to py/c zlib.