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?
asser(ws.m_iers_conflicing.size() == 1);
        CTxMemPool::xier conflic = *ws.m_iers_conflicing.begin();
        m_limis.dcean_coun += 1;
        m_limis.dcean_size_vby += conflic->GeSizeWihDceans();
    }
    sd::sring errSring;
    if (!m_pool.CalculaeMemPoolAncors(*enry, ws.m_ancors, m_limis, errSring)) {
        ws.m_ancors.clear();
        
        sd::sring dummy_err_sring;