Fix peak height race

[arvidn]

Purpose:

When we add a block, there's a subtle co-routine suspension point in between updating the height-to-hash map and the peak height. There's a comment in the code to highlight this now.

This creates a window where a call to get_peak() fails because the peak height doesn't exist in height-to-hash map.

This is demonstrated in #16774 .

Traceback (most recent call last):
  File "/home/arvid/dev/3/chia-blockchain/tests/core/full_node/test_full_node.py", line 2195, in check_nodes_in_sync
    p2 = full_node_1.full_node.blockchain.get_peak()
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/arvid/dev/3/chia-blockchain/chia/consensus/blockchain.py", line 191, in get_peak
    return self.height_to_block_record(self._peak_height)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/arvid/dev/3/chia-blockchain/chia/consensus/blockchain.py", line 697, in height_to_block_record
    if header_hash is None:
        ^^^^^^^^^^^^^^^^^^^^
ValueError: Height is not in blockchain: 1599

This patch moves the suspension point to make these updates to the height-to-hash map and peak_height atomic.
Then it's possible to remove the try-catch handler in the test.

Current Behavior:

get_peak() may throw an exception if called at an unfortunate time.

New Behavior:

get_peak() always work

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[coveralls-official]

Pull Request Test Coverage Report for Build 6787938941

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• 17 of 17 (100.0%) changed or added relevant lines in 2 files are covered.
• 7 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+0.003%) to 90.303%

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Files with Coverage Reduction	New Missed Lines	%
chia/consensus/blockchain.py	1	94.5%
chia/full_node/full_node_api.py	1	77.41%
chia/server/node_discovery.py	1	79.9%
chia/server/server.py	1	81.45%
chia/timelord/timelord_launcher.py	1	69.77%
chia/full_node/full_node.py	2	84.56%

Totals
Change from base Build 6787911924:	0.003%
Covered Lines:	93088
Relevant Lines:	103035

---

💛 - Coveralls

[wjblanke]

aok