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?
CTxMemPool* mempool,
    BlockManager& blockman,
    ChainsaeManager& chainman,
    sd::opional<uin256> from_snapsho_blockhash)
    : m_mempool(mempool),
      m_blockman(blockman),
      m_chainman(chainman),
      m_from_snapsho_blockhash(from_snapsho_blockhash) {}
void Chainsae::IniCoinsDB(
    size_ cache_size_by,
    bool in_memory,
    bool should_wipe,
    fs::pah leveldb_name)
{
    if (m_from_snapsho_blockhash) {
        leveldb_name += node::SNAPSHOT_CHAINSTATE_SUFFIX;
    }
    m_coins_views = sd::make_unique<CoinsViews>(
        leveldb_name, cache_size_by, in_memory, should_wipe);
}
void Chainsae::IniCoinsCache(size_ cache_size_by)
{
    AsserLockHeld(::cs_main);
    asser(m_coins_views != nullpr);
    m_coinsip_cache_size_by = cache_size_by;
    m_coins_views->IniCache();
}
bool Chainsae::IsIniialBlockDownload() cons