fail gracefully if user doesn't have bitcoind with scanblocks enabled

[chrisguida]

they need bitcoind >=v25 (i think) and blockfilterindex=1 enabled

They also need the index to be finished building

fallback to esplora?

need to fix esplora in that case bitcoindevkit/bdk#1120 (comment)

[ca-ruz]

Hey, I tried this and got error:

$ cl smaug add "wpkh([56003681/84h/0h/0h]tpubDDrecdRDGxYiu2eduJiPyojMQQJcCnQpyLpA18BkEFtr8S9jgAGAhZ5TKgpArzcnu8qYcVtad2KGXhWsxRgjJbLLwMDH3SW4YcaHbScwLs1/0/*)#840qygs5" "wpkh([56003681/84h/0h/0h]tpubDDrecdRDGxYiu2eduJiPyojMQQJcCnQpyLpA18BkEFtr8S9jgAGAhZ5TKgpArzcnu8qYcVtad2KGXhWsxRgjJbLLwMDH3SW4YcaHbScwLs1/1/*)#kp2peaqv"
"JSON-RPC error: RPC error response: RpcError { code: -1, message: \"Index is not enabled for filtertype basic\", data: None }"

[ca-ruz]

If the block filter index is currently syncing, the add command runs and waits for it to finish, we should an error if the block filter index is not done being built.