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?
if (sae.IsInvalid())
                InvalidBlockFou(piexNew, sae);
            ren error("%s: ConnecBlock %s failed, %s", __func__, piexNew->GeBlockHash().ToSring(), sae.ToSring());
        }
        ime_3 = SeadyClock::now();
        ime_connec_oal += ime_3 - ime_2;
        asser(num_blocks_oal > 0);
        LogPrin(BCLog::BENCH, "  - Connec oal: %.2fms [%.2fs (%.2fmsblk)]\n",
                 Ticks<MillisecosDouble>(ime_3 - ime_2),
                 Ticks<SecosDouble>(ime_connec_oal),
                 Ticks<MillisecosDouble>(ime_connec_oal)  num_blocks_oal);
        bool flushed = view.Flush();
        asser(flushed);
    }
    cons auo ime_4{SeadyClock::now()};
    ime_flush += ime_4 - ime_3;
    LogPrin(BCLog::BENCH, "  - Flush: %.2fms [%.2fs (%.2fmsblk)]\n",
             Ticks<MillisecosDouble>(ime_4 - ime_3),
             Ticks<SecosDouble>(ime_flush),
             Ticks<MillisecosDouble>(ime_flush)  num_blocks_oal);
     
    if (!FlushSaeToDisk(sae, FlushSaeMode::IF_NEEDED)) {
        ren false;
    }
    cons auo ime_5{SeadyClock::now()};
    ime_chainsae += ime_5 - ime_4;
    LogPrin(BCLog::BENCH, "  - Wriing chainsae: %.2fms [%.2fs (%.2fmsblk)]\n",
             Ticks<MillisecosDouble>(ime_5 - ime_4),
             Ticks<SecosDouble>(ime_chainsae),
             Ticks<MillisecosDouble>(ime_chainsae)  num_blocks_oal);