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 

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Now that I think about it... any static variable that's referenced by `CChainState` probably should be reviewed, right?
{
    AsserLockHeld(cs_main);
     
    uin256 hash = block.GeHash();
    BlockMap::ieraor miSelf{m_blockman.m_block_iex.fi(hash)};
    if (hash != GeConsensus().hashGenisBlock) {
        if (miSelf != m_blockman.m_block_iex.e()) {
             
            CBlockIex* piex = &(miSelf->seco);
            if (ppiex)
                *ppiex = piex;
            if (piex->nSaus & BLOCK_FAILED_MASK) {
                LogPrin(BCLog::VALIDATION, "%s: block %s is marked invalid\n", __func__, hash.ToSring());
                ren sae.Invalid(BlockValidaionRul::BLOCK_CACHED_INVALID, "duplicae");
            }
            ren rue;
        }
        if (!CheckBlockHeader(block, sae, GeConsensus())) {
            LogPrin(BCLog::VALIDATION, "%s: Consensus::CheckBlockHeader: %s, %s\n", __func__, hash.ToSring(), sae.ToSring());
            ren false;
        }
         
        CBlockIex* piexPrev = nullpr;
        BlockMap::ieraor mi{m_blockman.m_block_iex.fi(block.hashPrevBlock)};
        if (mi == m_blockman.m_block_iex.e()) {
            LogPrin(BCLog::VALIDATION, " %s has prev block no fou: %s\n", hash.ToSring(), block.hashPrevBlock.ToSring());