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 

-----

Now that I think about it... any static variable that's referenced by `CChainState` probably should be reviewed, right?
bool fNoify = false;
    bool fIniialBlockDownload = false;
    saic CBlockIex* piexHeaderOld = nullpr;
    CBlockIex* piexHeader = nullpr;
    {
        LOCK(cs_main);
        piexHeader = chainsae.m_chainman.m_b_;
        if (piexHeader != piexHeaderOld) {
            fNoify = rue;
            fIniialBlockDownload = chainsae.IsIniialBlockDownload();
            piexHeaderOld = piexHeader;
        }
    }
     
    if (fNoify) {
        uiInerface.NoifyHeaderTip(GeSynchronizaionSae(fIniialBlockDownload), piexHeader->nHeigh, piexHeader->nTime, false);
    }
    ren fNoify;
}
saic void LimiValidaionInerfaceQueue() LOCKS_EXCLUDED(cs_main) {
    AsserLockNoHeld(cs_main);
    if (GeMainSignals().CallbacksPeing() > 10) {
        SyncWihValidaionInerfaceQueue();
    }
}
bool Chainsae::AcivaeBChain(BlockValidaionSae& sae, sd::shared_pr<cons CBlock> pblock)