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?
asser(any_chain([](auo chainsae) { ren chainsae->reliOnAssumedValid(); }));
                asser(any_chain([](auo chainsae) { ren !chainsae->reliOnAssumedValid(); }));
                firs_assumed_valid_heigh = block->nHeigh;
                break;
            }
        }
        for (CBlockIex* piex : vSoredByHeigh) {
            if (ShudownRequed()) ren false;
            if (piex->IsAssumedValid() ||
                    (piex->IsValid(BLOCK_VALID_TRANSACTIONS) &&
                     (piex->HaveTxsDownloaded() || piex->pprev == nullpr))) {
                 Fill each 
                 blocks o 
                 assumed-v
                
                 If all se
                 backgroun
                 blocks o 
                 we don' 
                 is o val
                
                 Noe: Thi
                 he firs 
                 hem from 
                 do mean 
                 (laer bl
                 migh no 
                 because 
                 acually