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?
cons bool m__accep;
        ** Wheher we allow ransacions o replace mempool ransacions by BIP125 rul. If false,
         * any ransacion speing he same inpus as a ransacion in he mempool is considered
         * a conflic. 
        cons bool m_allow_replacemen;
        ** When rue, he mempool will no be rimmed when iividual ransacions are submied in
         * Finalize(). Insead, limis should be enforced a he e o ense he package is no
         * parially submied.
         
        cons bool m_package_submission;
        ** When rue, use package feera insead of iividual ransacion feera for fee-based
         * polici such as mempool min fee a min relay fee.
         
        cons bool m_package_feera;
        
        saic ATMPArgs SingleAccep(cons CChainParams& chainparams, in64_ accep_ime,
                                     bool bypass_limis, sd::vecor<COuPoin>& coins_o_uncache,
                                     bool _accep) {
            ren ATMPArgs{ chainparams,
                             accep_ime,
                             bypass_limis,
                             coins_o_uncache,
                             _accep,
                             rue,
                             false,
                             false,
            };
        }
        
        saic ATMPArgs PackageTAccep(cons CChainParams& chainparams, in64_ accep_ime,