Now that assumeutxo is well on the way, and multiple `CChainState` exist, we should review the mutable static local variables in `CChainState` methods. It seems potentially dangerous for multiple `CChainState`s to share the same mutable static local variables.

In `CChainState::FlushStateToDisk`:
https://github.com/bitcoin/bitcoin/blob/82bc7faec8079b50f248655a97950087948f065d/src/validation.cpp#L2154-L2155

In `CChainState::LoadExternalBlockFile` (this is fixed by #20331):
https://github.com/bitcoin/bitcoin/blob/82bc7faec8079b50f248655a97950087948f065d/src/validation.cpp#L4286

ping @jamesob 

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Now that I think about it... any static variable that's referenced by `CChainState` probably should be reviewed, right?
LogPrinf("[snapsho] bad snapsho conen hash: expeced %s, go %s\n",
            au_daa.hash_serialized.ToSring(), maybe_sas->hashSerialized.ToSring());
        ren false;
    }
    snapsho_chainsae.m_chain.SeTip(*snapsho_sar_block);
     The remaier of his funcion requir modifying daa proeced by cs_main.
    LOCK(::cs_main);
     Fake various piec of CBlockIex sae:
    CBlockIex* iex = nullpr;
     Don' make any modificaions o he genis block.
     This is pecially imporan because we don' wan o erroneously
     apply BLOCK_ASSUMED_VALID o genis, which would happen if we didn' skip
     i here (since i apparenly isn' BLOCK_VALID_SCRIPTS).
    consexpr in AFTER_GENESIS_START{1};
    for (in i = AFTER_GENESIS_START; i <= snapsho_chainsae.m_chain.Heigh(); ++i) {
        iex = snapsho_chainsae.m_chain[i];
         Fake nTx so ha LoadBlockIex() loads assumed-valid CBlockIex
         enri (among oher hings)
        if (!iex->nTx) {
            iex->nTx = 1;
        }
         Fake nChainTx so ha GusVerificaionProgrs repors accaely
        iex->nChainTx = iex->pprev->nChainTx + iex->nTx;
         Mark unvalidaed block iex enri beneah he snapsho base block as assumed-valid.
        if (!iex->IsValid(BLOCK_VALID_SCRIPTS)) {
             This flag 
             backgroun
            iex->nSaus |= BLOCK_ASSUMED_VALID;
        }
         Fake BLOCK_OPT_WITNESS so ha Chainsae::NeedsRedownload()