fix(forknet): Fix fork-network tool backward compatibility

[marcelo-gonzalez]

#12938 changed the format of the data we write to the FORK_TOOL Misc column keys in the init command, but didn't keep backward compatibility. But this should have been done because we need to run fork-network again when starting a forknet so we can run the set-validators and finalize commands. So this PR reads the values the old way if there's nothing in the FORK_TOOL_FLAT_HEAD key

[marcelo-gonzalez]

Tested with

$ git checkout ac5aa6a366306b1e33061e3008975bd7cb97ff4f~
$ cargo build -p neard
$ python3 tests/sanity/transactions.py
$ python3 tests/mocknet/local_test_node.py local-test-setup --source-home-dir ~/.near/test4_finished --target-home-dir ~/.near/test4_finished --neard-binary-path ~/nearcore/target/debug/neard --num-nodes 1 --yes
$ git checkout master
$ cargo build -p neard
$ cp ~/nearcore/target/debug/neard ~/.near/local-mocknet/node0/neard-runner/binaries/neard0
$ python3 tests/mocknet/mirror.py --local-test new-test --epoch-length 100 --num-validators 1 --num-seats 2 --new-chain-id foonet --genesis-protocol-version 76 --stateless-setup --yes
$ cat ~/.near/local-mocknet/node0/stderr
...
thread 'main' panicked at tools/fork-network/src/cli.rs:552:77:
called `Option::unwrap()` on a `None` value
...
$ git checkout $good_commit # good commit is this PR plus https://github.com/marcelo-gonzalez/nearcore/commit/f567b7bd67a6c4aab3cc1f1e9cbf450e4aa85f9d
$ cargo build -p neard
$ cp ~/nearcore/target/debug/neard ~/.near/local-mocknet/node0/neard-runner/binaries/neard0
$ python3 tests/mocknet/mirror.py --local-test new-test --epoch-length 100 --num-validators 1 --num-seats 2 --new-chain-id foonet --genesis-protocol-version 76 --stateless-setup --yes
$ python3 tests/mocknet/mirror.py --local-test start-nodes
$ curl localhost:3041/status | jq .sync_info
<GOOD>

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 49 lines in your changes missing coverage. Please review.

Project coverage is 70.23%. Comparing base (a0b4946) to head (0641f54).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
tools/fork-network/src/cli.rs	0.00%	49 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12964      +/-   ##
==========================================
- Coverage   70.25%   70.23%   -0.02%     
==========================================
  Files         855      855              
  Lines      176300   176341      +41     
  Branches   176300   176341      +41     
==========================================
- Hits       123860   123856       -4     
- Misses      47290    47329      +39     
- Partials     5150     5156       +6     

Flag	Coverage Δ
backward-compatibility	0.35% <0.00%> (-0.01%)	⬇️
db-migration	0.35% <0.00%> (-0.01%)	⬇️
genesis-check	1.41% <0.00%> (-0.01%)	⬇️
linux	69.85% <0.00%> (-0.01%)	⬇️
linux-nightly	69.86% <0.00%> (-0.05%)	⬇️
pytests	1.72% <0.00%> (-0.01%)	⬇️
sanity-checks	1.53% <0.00%> (-0.01%)	⬇️
unittests	70.07% <0.00%> (-0.02%)	⬇️
upgradability	0.35% <0.00%> (-0.01%)	⬇️

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[Longarithm]

@Trisfald may I ask you for review because you reviewed the original change?

[Trisfald]

Great, thanks!

I'm fine with this change just tested manually

[Trisfald]

nit: These three keys (b"FORK_TOOL_EPOCH_ID", etc) now appear multiple times, we could use a constant

[marcelo-gonzalez]

done