core: fix header copy race

[taratorio]

relates to #13480
fully fixes #13474

Seems like Header.hash memoization changes from a few months ago have made Block.Header() (which makes a copy by calling CopyHeader) show race warnings. This is because we are copying over atomic.Pointer in CopyHeader.

This PR fixes this by manually copy-ing all fields and skipping copy of the hash atomic.Pointer attribute (instead it will get set using its zero value - correct behaviour) and then the hash will be memoized using it as part of the copy later on.

This is a bit clumsier as we can miss updating the CopyHeader function when adding new attributes to the Header struct - to address that I've added a reflection based test which will generate random values for all struct fields and as a result capture this pitfall and remind developers to update.

Example race detected:

==================
WARNING: DATA RACE
Read at 0x00c03acc0838 by goroutine 26498:
  github.com/erigontech/erigon/core/types.CopyHeader()
      /home/ubuntu/erigon/core/types/block.go:1098 +0x5c
  github.com/erigontech/erigon/core/types.(*Block).Header()
      /home/ubuntu/erigon/core/types/block.go:1278 +0x54
  github.com/erigontech/erigon/turbo/execution/eth1/eth1_utils.ConvertBlockToRPC()
      /home/ubuntu/erigon/turbo/execution/eth1/eth1_utils/grpc.go:108 +0x55
  github.com/erigontech/erigon/turbo/execution/eth1/eth1_utils.ConvertBlocksToRPC()
      /home/ubuntu/erigon/turbo/execution/eth1/eth1_utils/grpc.go:102 +0xc4
  github.com/erigontech/erigon/polygon/sync.(*executionClient).InsertBlocks()
      /home/ubuntu/erigon/polygon/sync/execution_client.go:71 +0x4f
  github.com/erigontech/erigon/polygon/sync.(*ExecutionClientStore).insertBlocks()
      /home/ubuntu/erigon/polygon/sync/store.go:162 +0x14f
  github.com/erigontech/erigon/polygon/sync.(*ExecutionClientStore).Run()
      /home/ubuntu/erigon/polygon/sync/store.go:143 +0x1ab
  github.com/erigontech/erigon/polygon/sync.(*Service).Run.func2()
      /home/ubuntu/erigon/polygon/sync/service.go:125 +0x69
  golang.org/x/sync/errgroup.(*Group).Go.func1()
==================