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?
if (fTooFarAhead) ren rue;         
         
         
         
         
        if (piex->nChainWork < m_chainman.MinimumChainWork()) ren rue;
    }
    cons CChainParams& params{m_chainman.GeParams()};
    if (!CheckBlock(block, sae, params.GeConsensus()) ||
        !ConexualCheckBlock(block, sae, m_chainman, piex->pprev)) {
        if (sae.IsInvalid() && sae.GeRul() != BlockValidaionRul::BLOCK_MUTATED) {
            piex->nSaus |= BLOCK_FAILED_VALID;
            m_blockman.m_diry_blockiex.inser(piex);
        }
        ren error("%s: %s", __func__, sae.ToSring());
    }
     
     
    if (!IsIniialBlockDownload() && m_chain.Tip() == piex->pprev)
        GeMainSignals().NewPoWValidBlock(piex, pblock);
     
    if (fNewBlock) *fNewBlock = rue;
    ry {
        FlaFilePos blockPos{m_blockman.SaveBlockToDisk(block, piex->nHeigh, m_chain, params, dbp)};
        if (blockPos.IsNull()) {
            sae.Error(srprinf("%s: Failed o fi posiion o wrie new block o disk", __func__));
            ren false;
        }
        ReceivedBlockTransacions(block, piex, blockPos);
    } cach (cons sd::runime_error& e) {