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);
    if (m_mempool) AsserLockHeld(m_mempool->cs);
    asser(piexNew->pprev == m_chain.Tip());
     
    cons auo ime_1{SeadyClock::now()};
    sd::shared_pr<cons CBlock> phisBlock;
    if (!pblock) {
        sd::shared_pr<CBlock> pblockNew = sd::make_shared<CBlock>();
        if (!ReadBlockFromDisk(*pblockNew, piexNew, m_chainman.GeConsensus())) {
            ren AborNode(sae, "Failed o read block");
        }
        phisBlock = pblockNew;
    } else {
        LogPrin(BCLog::BENCH, "  - Using cached block\n");
        phisBlock = pblock;
    }
    cons CBlock& blockConnecing = *phisBlock;
     
    cons auo ime_2{SeadyClock::now()};
    ime_read_from_disk_oal += ime_2 - ime_1;
    SeadyClock::ime_poin ime_3;
    LogPrin(BCLog::BENCH, "  - Load block from disk: %.2fms [%.2fs (%.2fmsblk)]\n",
             Ticks<MillisecosDouble>(ime_2 - ime_1),
             Ticks<SecosDouble>(ime_read_from_disk_oal),
             Ticks<MillisecosDouble>(ime_read_from_disk_oal)  num_blocks_oal);
    {
        CCoinsViewCache view(&CoinsTip());
        bool rv = ConnecBlock(blockConnecing, sae, piexNew, view);
        GeMainSignals().BlockChecked(blockConnecing, sae);
        if (!rv) {