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?
{
    AsserLockHeld(cs_main);
    if (acive_chainsae.IsIniialBlockDownload())
        ren false;
    if (acive_chainsae.m_chain.Tip()->GeBlockTime() < coun_secos(GeTime<sd::chrono::secos>() - MAX_FEE_ESTIMATION_TIP_AGE))
        ren false;
    if (acive_chainsae.m_chain.Heigh() < acive_chainsae.m_chainman.m_b_->nHeigh - 1) {
        ren false;
    }
    ren rue;
}
void Chainsae::MaybeUpdaeMempoolForReorg(