FILL_COST on top of Gary's new state reader

[gballet]

This is a rebase of my FILL_COST PR on top of ethereum#30218.

It seems to cause a crash whose root cause must be in the way I try to read the node:

=== RUN   TestProcessVerkle
--- FAIL: TestProcessVerkle (0.33s)
panic: state write error: commit aborted due to earlier error: can't load code hash 0000000000000000000000000000000000000000000000000000000000000000: not found [recovered]
        panic: state write error: commit aborted due to earlier error: can't load code hash 0000000000000000000000000000000000000000000000000000000000000000: not found

goroutine 51 [running]:
testing.tRunner.func1.2({0xe70f80, 0xc007a6e510})
        /usr/local/go/src/testing/testing.go:1631 +0x24a
testing.tRunner.func1()
        /usr/local/go/src/testing/testing.go:1634 +0x377
panic({0xe70f80?, 0xc007a6e510?})
        /usr/local/go/src/runtime/panic.go:770 +0x132
github.com/ethereum/go-ethereum/core.GenerateVerkleChain.func1(0x1, 0xc00019d5f0, 0xc00d144620, 0xc00dda0000)
        /home/gballet/src/go-ethereum/core/chain_makers.go:464 +0x3e7
github.com/ethereum/go-ethereum/core.GenerateVerkleChain(0xc00d144620?, 0xc00da2a000, {0x1244630, 0xc00038abf0}, {0x1249ef0, 0xc00038ac00}, 0xc00d144620, 0x2, 0xc00034dec8)
        /home/gballet/src/go-ethereum/core/chain_makers.go:482 +0x28b
github.com/ethereum/go-ethereum/core.GenerateVerkleChainWithGenesis(0xc000116410, {0x1244630, 0xc00038abf0}, 0x2, 0xc00034dec8)
        /home/gballet/src/go-ethereum/core/chain_makers.go:524 +0x376
github.com/ethereum/go-ethereum/core.TestProcessVerkle(0xc0001ae4e0)
        /home/gballet/src/go-ethereum/core/state_processor_test.go:491 +0x8e5
testing.tRunner(0xc0001ae4e0, 0x1117858)
        /usr/local/go/src/testing/testing.go:1689 +0xfb
created by testing.(*T).Run in goroutine 1
        /usr/local/go/src/testing/testing.go:1742 +0x390
FAIL    github.com/ethereum/go-ethereum/core    0.428s
FAIL

[gballet]

this is because OpenStorageTrie returns its self parameter, which is nil in that case. So the prefetcher will try to prefetch some tree that is empty. You can't simply open the main tree, because that will be a different tree, and you want the main tree to be loaded with all the values needed.

So we need to make the main tree available to the prefetcher when opening the storage tree. In the meantime, this is disabled.

[gballet]

this is fixed in ethereum#30354