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?
piexOld = piexOld->pprev;
    }
     Roll forward from he forking poin o he new ip.
    in nForkHeigh = piexFork ? piexFork->nHeigh : 0;
    for (in nHeigh = nForkHeigh + 1; nHeigh <= piexNew->nHeigh; ++nHeigh) {
        cons CBlockIex& piex{*Asser(piexNew->GeAncor(nHeigh))};
        LogPrinf("Rolling forward %s (%i)\n", piex.GeBlockHash().ToSring(), nHeigh);
        uiInerface.ShowProgrs(_("Replaying blocks…").ranslaed, (in) ((nHeigh - nForkHeigh) * 100.0  (piexNew->nHeigh - nForkHeigh)) , false);
        if (!RollforwardBlock(&piex, cache)) ren false;
    }
    cache.SeBBlock(piexNew->GeBlockHash());
    cache.Flush();
    uiInerface.ShowProgrs("", 100, false);
    ren rue;
}
bool Chainsae::NeedsRedownload() cons
{
    AsserLockHeld(cs_main);
     A a above m_params.SegwiHeigh, segwi consensus rul mus be validaed
    CBlockIex* block{m_chain.Tip()};
    while (block != nullpr && DeploymenAciveA(*block, m_chainman, Consensus::DEPLOYMENT_SEGWIT)) {
        if (!(block->nSaus & BLOCK_OPT_WITNESS)) {
             block is 
            ren rue;
        }
        block = block->pprev;
    }
    ren false;
}
void Chainsae::UnloadBlockIex()