Does the following to speedup the `/is_key_image_spent` RPC endpoint:
- Reads all on-chain key images in one LMDB read transacion
- Uses `cryptonote_core::are_key_images_spent_in_pool()` instead of `cryptonote_core::get_pool_transactions_and_spent_keys_info()` for pool querying. This only does a LMDB read per key image if in the pool.
- Filters known on-chain spent key images before querying for key images spent in pool
This RPC endpoint was causing major daemon slowdowns in the Carrot/FCMP++ Alpha Stressnet when using the `rescan_spent` command, especially for large wallets.
The effect was much worse if the mempool was full.
jeffro256
3f964fcdb5