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?
int64_t m_total_coinstip_cache{0};
    
    
    
    int64_t m_total_coinsdb_cache{0};
    
    
    
    
    Chainstate& InitializeChainstate(CTxMemPool* mempool) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
    
    std::vector<Chainstate*> GetAll();
    
    
    
    
    
    
    
    
    
    
    
    
    
    [[nodiscard]] bool ActivateSnapshot(
        AutoFile& coins_file, const node::SnapshotMetadata& metadata, bool in_memory);
    
    Chainstate& ActiveChainstate() const;
    CChain& ActiveChain() const EXCLUSIVE_LOCKS_REQUIRED(GetMutex()) { return ActiveChainstate().m_chain; }