* refactor test
* add a fast fixed examples test for the main suite
* split slow test for the integration suite

`cfg` is not a pointer

* speed up docker image build by use layer cache

* rearrenge Dockerfile

* enable docker layer cache in github action

Co-authored-by: Alexey Sharp <alexeysharp@Alexeys-iMac.local>

* print branchHash

* Print state changes

* Print val

* Fix for author

* Remove prints

Co-authored-by: Alexey Sharp <alexeysharp@Alexeys-iMac.local>

Co-authored-by: Alexey Sharp <alexeysharp@Alexeys-iMac.local>

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* Update stageloop.go

* Print

* Consider snapshot headers as parlia checkpoints

* Not fail after not loading snapshot

* Lazy snapshots

* Print number of validators

* More printing

* Use epoch instead of checkpoint interval

* Reduce logging

* Fix compilation

* Remove trace jump dest

* Fix lint

* Not store snapshots every epoch

* Separate snapshot for verification and finalisation

Co-authored-by: Alex Sharp <alexsharp@Alexs-MacBook-Pro.local>
Co-authored-by: Alexey Sharp <alexeysharp@Alexeys-iMac.local>

* exchange RLPx Hello even when maxpeers limit is reached
* bump MaxPendingPeers to increase the default handshake queue
  (and the likelyhood of Hello exchange)

The test was flaky, because of the "endpoint prediction".
The test starts 5 nodes one by one.
Node 0 is used as a bootstrap node for nodes 1-4.
When it is about to add, say, node 3, nodes 0 and 1 might already have had a chance to communicate,
and updateEndpoints() deletes the node 0 UDP port, because fallbackUDP port was not configured.

In this case node 3 would get a bootstrap node 0 without a port and lead to an error:

    v5_udp_test.go:110: bad bootstrap node "enr:...": missing UDP port

The problem was reproducible by this command:

    go test ./p2p/discover -run TestUDPv5_lookupE2E -count 500

* cmd/utils: initialize f.Value before setting variable

* override.terminaltotaldifficulty flag

* Add OverrideTerminalTotalDifficulty to default_flags

Problem: (nil, nil) from CountPingErrors was not handled.
This happens if the node is not in the db (a bootstrap node),
and was never crawled before.

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* Update reset_state.go

* Update reset_state.go

* reduce downloader deps

* reduce downloader deps

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* reduce downloader deps

* reduce downloader deps

* reduce downloader deps

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* use semaphore instead of a chan struct{}
* move MaxPendingPeers default value to DefaultConfig.P2P
* log Error if Accept fails
* replace quit channel with context

The test was slow, because it was trying to find
predefined nodeIDs (lookupTestnet) by generating random keys
and trying to find their neighbours
until it hits all nodes of the lookupTestnet.
In addition each FindNode response was waited for 0.5 sec (respTimeout).
This could take up to 30 sec and fail the test suite.

A fake random key generator is now used during the test.
It issues the expected keys, and the lookup converges quickly.
The reply timeout is reduced for the test.
Now it normally takes less than.1 sec.

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* Re-introduced cleanup of temporary table

* Fix sign

* Fix lint

* Fix lint

* Revert

Co-authored-by: Alex Sharp <alexsharp@Alexs-MacBook-Pro.local>

* Place finishHandlingForkChoice after startHandlingForkChoice

* forkChoiceMessage -> forkChoice

* Check that safe & finalized blocks are canonical for no-op forkChoice