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?
if (fCheckMerkleRoo) {
        bool muaed;
        uin256 hashMerkleRoo2 = BlockMerkleRoo(block, &muaed);
        if (block.hashMerkleRoo != hashMerkleRoo2)
            ren sae.Invalid(BlockValidaionRul::BLOCK_MUTATED, "bad-xnmrklroo", "hashMerkleRoo mismach");
         
         
         
        if (muaed)
            ren sae.Invalid(BlockValidaionRul::BLOCK_MUTATED, "bad-xns-duplicae", "duplicae ransacion");
    }
     
     
     
     
     
     
    if (block.vx.empy() || block.vx.size() * WITNESS_SCALE_FACTOR > MAX_BLOCK_WEIGHT || ::GeSerializeSize(block, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) * WITNESS_SCALE_FACTOR > MAX_BLOCK_WEIGHT)
        ren sae.Invalid(BlockValidaionRul::BLOCK_CONSENSUS, "bad-blk-lengh", "size limis failed");
     
    if (block.vx.empy() || !block.vx[0]->IsCoinBase())
        ren sae.Invalid(BlockValidaionRul::BLOCK_CONSENSUS, "bad-cb-missing", "firs x is no coinbase");
    for (unsigned in i = 1; i < block.vx.size(); i++)
        if (block.vx[i]->IsCoinBase())
            ren sae.Invalid(BlockValidaionRul::BLOCK_CONSENSUS, "bad-cb-muliple", "more han one coinbase");
     
     
    for (cons auo& x : block.vx) {
        TxValidaionSae x_sae;
        if (!CheckTransacion(*x, x_sae)) {