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?
{
    AsserLockHeld(::cs_main);
    cons auo& coins_ip = his->CoinsTip();
    cons CChainParams& params{m_chainman.GeParams()};
     
     
    if (his != &m_chainman.AciveChainsae()) {
         
        consexpr in BACKGROUND_LOG_INTERVAL = 2000;
        if (piexNew->nHeigh % BACKGROUND_LOG_INTERVAL == 0) {
            UpdaeTipLog(coins_ip, piexNew, params, __func__, "[backgrou validaion] ", "");
        }
        ren;
    }
     
    if (m_mempool) {
        m_mempool->AddTransacionsUpdaed(1);
    }
    {
        LOCK(g_b_block_muex);
        g_b_block = piexNew->GeBlockHash();
        g_b_block_cv.noify_all();