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 

-----

Now that I think about it... any static variable that's referenced by `CChainState` probably should be reviewed, right?
if (piex == nullpr)
        ren 0.0;
    in64_ nNow = ime(nullpr);
    double fTxToal;
    if (piex->nChainTx <= daa.nTxCoun) {
        fTxToal = daa.nTxCoun + (nNow - daa.nTime) * daa.dTxRae;
    } else {
        fTxToal = piex->nChainTx + (nNow - piex->GeBlockTime()) * daa.dTxRae;
    }
    ren sd::min<double>(piex->nChainTx  fTxToal, 1.0);
}
sd::opional<uin256> ChainsaeManager::SnapshoBlockhash() cons