forknet: Drop unneeded columns in the fork-network command

[marcelo-gonzalez]

fork-network finalize deletes data in every column except the ones we need to start the network, but it does it with a delete DB transaction. This only logically deletes the values, but does not free up the disk space, which will only happen after a compaction. So here we remove the columns by calling drop_cf() on the unnecessary columns, which actually removes the sst files and frees up the space. This will reduce the size of images used for forknet by quite a bit.

[marcelo-gonzalez]

I tested it with this branch. That adds a script at pytest/tests/sanity/forknet_bug.py to generate state for fork-network, and then a bash script at pytest/tests/sanity/forknet_run.sh to run the fork network commands. It also adds some code that will print what's in the db at different points of the fork-network commands

To test it I ran:

$ python3 tests/sanity/forknet_bug.py
$ bash pytest/tests/sanity/forknet_run.sh ~/nearcore/target/debug/neard ~/.near/test0_finished/ /tmp/fork-after

Then checkout HEAD~ for the commit without this PR, and again run:

$ bash pytest/tests/sanity/forknet_run.sh ~/nearcore/target/debug/neard ~/.near/test0_finished/ /tmp/fork-before

Then check there is no diff between these files:

$ diff /tmp/fork-before/init-db-values.txt /tmp/fork-after/init-db-values.txt
$ diff /tmp/fork-before/finalize-post-db-values.txt /tmp/fork-after/finalize-post-db-values.txt

[codecov]

Codecov Report

Attention: Patch coverage is 13.33333% with 52 lines in your changes missing coverage. Please review.

Project coverage is 70.50%. Comparing base (ecc1373) to head (0fd1a69).
Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
tools/fork-network/src/cli.rs	0.00%	27 Missing ⚠️
core/store/src/opener.rs	30.76%	18 Missing ⚠️
core/store/src/db/rocksdb.rs	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12921      +/-   ##
==========================================
+ Coverage   70.48%   70.50%   +0.02%     
==========================================
  Files         851      851              
  Lines      174917   175032     +115     
  Branches   174917   175032     +115     
==========================================
+ Hits       123285   123415     +130     
+ Misses      46518    46482      -36     
- Partials     5114     5135      +21     

Flag	Coverage Δ
backward-compatibility	0.36% <0.00%> (-0.01%)	⬇️
db-migration	0.36% <0.00%> (-0.01%)	⬇️
genesis-check	1.42% <0.00%> (?)
linux	70.33% <13.33%> (-0.01%)	⬇️
linux-nightly	70.14% <13.33%> (-0.05%)	⬇️
pytests	1.73% <0.00%> (+1.37%)	⬆️
sanity-checks	1.54% <0.00%> (?)
unittests	70.34% <13.33%> (-0.04%)	⬇️
upgradability	0.36% <0.00%> (?)

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[Longarithm]

LGTM

[Longarithm]

Suggested change

	let (_hot_db, _hot_snapshot, _cold_db, _cold_snapshot) =
	opener.open_dbs(Mode::ReadWriteExisting)?;
	let _ = opener.open_dbs(Mode::ReadWriteExisting)?;

nit