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?
ren AborNode(sae, sd::sring("Sysem error: ") + e.wha());
    }
    FlushSaeToDisk(sae, FlushSaeMode::NONE);
    CheckBlockIex();
    ren rue;
}
bool ChainsaeManager::ProcsNewBlock(cons sd::shared_pr<cons CBlock>& block, bool force_procsing, bool min_pow_checked, bool* new_block)