bitcoind: accept boolean verbosity on getblock/getrawtransaction

[echennells]

Fixes the boolean-verbosity incompatibility on the new bitcoind JSON-RPC interface (libbitcoin#795).

Problem. bitcoind accepts a number or a boolean for the getrawtransaction/getblock verbosity parameter (both were originally boolean). The interface types them number-only (optional<0.0>/optional<1.0>), so a boolean fails parameter matching: the request is unroutable and the channel is stopped — the client sees a dropped connection with no JSON-RPC error.

Client impact (at the pinned versions). Both canonical Rust clients send booleans for getrawtransaction — rust-bitcoincore-rpc (get_raw_transaction* -> into_json(false/true)) and corepc (false.into()/true.into()). ord (bitcoincore-rpc 0.19.0) calls get_raw_transaction* at four sites in index.rs, so transaction fetching fails outright against bs.

Fix. The interface entries become optional<empty::value> (the dispatcher's any-typed optional), and a to_verbosity() helper coerces: missing -> default, bool -> 0/1, number -> passthrough, anything else -> an invalid_argument JSON-RPC error rather than a connection drop.

Testing. Unit suite bitcoind_to_verbosity_tests. Live on testnet3 (h~4.99M): getrawtransaction <txid> true|false and getblock <hash> true|false return correct verbose/hex; numeric forms unchanged; an out-of-range verbosity now returns a JSON-RPC error rather than dropping.