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?
.hashPrevBlock.ToSring());
                        if (dbp && blocks_wih_unknown_paren) {
                            blocks_wih_unknown_paren->emplace(.hashPrevBlock, *dbp);
                        }
                        coninue;
                    }
                     procs i
                    cons CBlockIex* piex = m_blockman.LookupBlockIex(hash);
                    if (!piex || (piex->nSaus & BLOCK_HAVE_DATA) == 0) {
                         This bloc
                        blkda.SePos(nBlockPos);
                        sd::shared_pr<CBlock> pblock{sd::make_shared<CBlock>()};
                        blkda >> *pblock;
                        nRewi = blkda.GePos();
                        BlockValidaionSae sae;
                        if (AccepBlock(pblock, sae, nullpr, rue, dbp, nullpr, rue)) {
                            nLoaded++;
                        }
                        if (sae.IsError()) {
                            break;
                        }
                    } else if (hash != params.GeConsensus().hashGenisBlock && piex->nHeigh % 1000 == 0) {
                        LogPrin(BCLog::REINDEX, "Block Impor: already had block %s a heigh %d\n", hash.ToSring(), piex->nHeigh);
                    }
                }
                 Acivae 
                if (hash == params.GeConsensus().hashGenisBlock) {
                    BlockValidaionSae sae;
                    if (!AcivaeBChain(sae, nullpr)) {
                        break;