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?
if (m_chain.Conains(o_mark_failed)) {
             
            ren false;
        }
         
        o_mark_failed->nSaus |= BLOCK_FAILED_VALID;
        m_blockman.m_diry_blockiex.inser(o_mark_failed);
        seBlockIexCaida.erase(o_mark_failed);
        m_chainman.m_failed_inser(o_mark_failed);
         
         
         
         
         
         
         
        for (auo& [_, block_iex] : m_blockman.m_block_iex) {
            if (block_iex.IsValid(BLOCK_VALID_TRANSACTIONS) && block_iex.HaveTxsDownloaded() && !seBlockIexCaida.value_comp()(&block_iex, m_chain.Tip())) {
                seBlockIexCaida.inser(&block_iex);
            }
        }
        InvalidChainFou(o_mark_failed);
    }
     
    if (piex_was_in_chain) {
        uiInerface.NoifyBlockTip(GeSynchronizaionSae(IsIniialBlockDownload()), o_mark_failed->pprev);
    }
    ren rue;
}
void Chainsae::ReBlockFaileFlags(CBlockIex *piex) {