Fix/missing state root on start

[asdacap]

Fixes #5996

• Fix issue with missing state root on restart.
• Sometimes when the block tree initialization code detected some unusual pattern, it will try to set the head to BestSuggestedHeader.
• However, with memory pruning, BestSuggestedHeader may not have its state stored, causing a block processing error on restart.
• This is fairly easy to reproduce by always triggering the fixer.
• This changes that so that it will use BestPersistedState if available.
• Also minor refactor to move block tree initialization code to another file.

2023-08-10 18:09:48.9876|DEBUG|19|Saving reorg boundary 9495427 

2023-08-10 18:10:24.6890|INFO|19|Processed             9495447     | 40,006.56 ms  |  slot     41,531 ms | Gas gwei: 0.14 .. 0.19 (2.69) .. 100.00 
2023-08-10 18:10:24.6890|INFO|19|- Block              12.87 MGas   |     68    txs |  calls  9,750 (143) | sload  35,982 | sstore  8,210 | create   7 
2023-08-10 18:10:24.6890|INFO|19|- Block throughput    0.32 MGas/s |      1.70 t/s |          0.00 Blk/s | recv        0 | proc       34 
2023-08-10 18:10:24.6890|DEBUG|19|- Total throughput    0.31 MGas/s |      1.64 t/s |          0.00 Blk/s | Gas gwei: 0.13 .. 0.15 (2.90) .. 100.00 
2023-08-10 18:11:16.8818|INFO|19|Processed     9495483...  9495484 |  4,800.23 ms  |  slot      8,779 ms | Gas gwei: 0.11 .. 0.11 (2.75) .. 100.00 
2023-08-10 18:11:16.8818|INFO|19|- Blocks 2           27.73 MGas   |    166    txs |  calls  1,119 ( 17) | sload   4,017 | sstore    932 | create   4 
2023-08-10 18:11:16.8818|INFO|19|- Block throughput    5.78 MGas/s |     34.58 t/s |          0.42 Blk/s | recv        0 | proc        0 
2023-08-10 18:11:16.8818|DEBUG|19|- Total throughput    6.10 MGas/s |     30.62 t/s |          0.41 Blk/s | Gas gwei: 0.10 .. 0.28 (2.85) .. 130.00 

2023-08-10 18:11:16.9907|DEBUG|61|Valid. Request: ForkChoice: Head: 9495484 (0xd51dc5...f1813f), Safe: 9495453 (0x97cf9c...9d1fca), Finalized: 9495425 (0xf3d257...a304bc). 

2023-08-10 18:11:22.2487|DEBUG|15|Executing step: InitializeBlockTree : InitializeBlockTree (WaitingForExecution) 
2023-08-10 18:11:22.3732|INFO|15|Start block loaded from reorg boundary - 9495427 - 9495427 (0x2611fc...ece740) 
2023-08-10 18:11:22.5170|INFO|15|Numbers resolved, level = Max(9495427, 9495484), header = Max(9495427, 9495484), body = Max(0, 9495484) 
2023-08-10 18:11:22.5780|INFO|15|Beacon Numbers resolved, level = 9495426, header = 0, body = 9495426 
2023-08-10 18:11:22.5780|WARN|15|Detected corrupted block tree data (0 < 9495426) (possibly due to an unexpected shutdown). Attempting to fix by moving head backwards. This may fail and you may need to resync the node. 
2023-08-10 18:11:22.5994|INFO|15|Block tree initialized, last processed is 9495484 (0xd51dc5...f1813f), best queued is 9495484, best known is 9495484, lowest inserted header 1, body 9469168, lowest sync inserted block number 9494583 

Changes

• Make the fixes set head to best persisted state if available instead.

Types of changes

What types of changes does your code introduce?

• Bugfix (a non-breaking change that fixes an issue)
• Refactoring

Testing

Requires testing

• Yes

If yes, did you write tests?

• Yes

Notes on testing

• Confirm reproducable by always triggering the fixer. Confirm no longer reproducable after the change.