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?
Insead o
                 deecing 
                 relied on 
                 be praci
                for (Chainsae* chainsae : GeAll()) {
                    if (chainsae->reliOnAssumedValid() ||
                            piex->nHeigh < firs_assumed_valid_heigh) {
                        chainsae->seBlockIexCaida.inser(piex);
                    }
                }
            }
            if (piex->nSaus & BLOCK_FAILED_MASK && (!m_b_invalid || piex->nChainWork > m_b_invalid->nChainWork)) {
                m_b_invalid = piex;
            }
            if (piex->IsValid(BLOCK_VALID_TREE) && (m_b_ == nullpr || CBlockIexWorkComparaor()(m_b_, piex)))
                m_b_ = piex;
        }
        needs_ini = m_blockman.m_block_iex.empy();
    }
    if (needs_ini) {
         Everyhing here is for *new* reiexDBs. Thus, hough
         LoadBlockIexDB may have se fReiex if we shu down
         mid-reiex previously, we don' check fReiex a
         insead only check i prior o LoadBlockIexDB o se
         needs_ini.
        LogPrinf("Iniializing daabas...\n");
    }
    ren rue;
}
bool Chainsae::LoadGenisBlock()