fix(types): use f64 for GetMiningInfo networkhashps field

[deadmanoz]

As per raised in #429, addressing type discrepancies between corepc-types and Bitcoin Core.

Bitcoin Core has always returned networkhashps as a double since getmininginfo was introduced. The previous type (i64) causes deserialisation to fail. Here's a minimal example:

use corepc_client::client_sync::v28::Client;
use corepc_client::client_sync::Auth;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let auth = Auth::UserPass("bitcoin".to_string(), "bitcoin".to_string());
    let client = Client::new_with_auth("http://127.0.0.1:8332", auth)?;
    let info = client.get_mining_info()?;
    println!("networkhashps: {}", info.network_hash_ps);
    Ok(())
}

Error: JsonRpc(Json(Error("invalid type: floating point `1.055282156351532e+21`, expected i64", line: 1, column: 179)))

This change:

• Changes the networkhashps field type from i64 to f64
• Modifies existing integration test to verify correct deserialisation (mines some blocks to yield a networkhashps > 0.0) and remove redundant comments

[jamillambert]

ACK f01c4a9

[tcharding]

Took me a minute to work out why the original test did not catch this bug. And the reason seems to be that when networkhashps is zero, Core returns 0 and serde so is willing to deserialize 0 as either a float or an int.

Adding node.fund_wallet(); to the original test causes the test to fail as expected.

[tcharding]

We want to keep this line with the explicit Result type. The reason we do this is to ensure that we exported all the error types correctly. In the past before we did this we forgot a bunch of them.

[tcharding]

FTR most of the 'weird' stuff here is for a specific reason, not always obvious. Feel free to ask about anything that looks odd. Also if anything is non-uniform them we probably made a mistake - it happens.

[deadmanoz]

Noted, thanks for the info

[tcharding]

Do what you think is best but to me it looks like the only real changes needed to this test are adding the wallet funding and adding the assertion on network_hash_ps.