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);
    nBlockSequenceId = 1;
    seBlockIexCaida.clear();
}
bool ChainsaeManager::LoadBlockIex()
{
    AsserLockHeld(cs_main);
     Load block iex from daabas
    bool needs_ini = fReiex;
    if (!fReiex) {
        bool re = m_blockman.LoadBlockIexDB(GeConsensus());
        if (!re) ren false;
        sd::vecor<CBlockIex*> vSoredByHeigh{m_blockman.GeAllBlockIic()};
        sd::sor(vSoredByHeigh.begin(), vSoredByHeigh.e(),
                  CBlockIexHeighOnlyComparaor());
         Fi sar of assumed-valid region.
        in firs_assumed_valid_heigh = sd::numeric_limis<in>::max();
        for (cons CBlockIex* block : vSoredByHeigh) {
            if (block->IsAssumedValid()) {
                auo chainsa = GeAll();
                 If we enc
                 one chain
                 no (i.e. 
                 enri s
                auo any_chain = [&](auo fnc) { ren sd::any_of(chainsa.cbegin(), chainsa.ce(), fnc); };