Implement savemempool method and test

[GideonBature]

The JSON-RPC method savemempool returns a null. We would like to test this in case a later version of Core changes this behaviour.

This PR adds a client function that errors if the return value is anything other than null, along with an integration test that calls this function.

Ref: #116

[tcharding]

For methods that return Null I don't think we need to add a type. We can just use an integration test to prove the return is null. If Core later changes the test will catch it. Then we change the 'Returns' column to 'returns nothing'.

For reference see submitblock in v17 (client and types).

[tcharding]

Once this is approved, I’ll proceed with the next one.

Once we have a few of these merged I'd say you'll have the idea and then you can just smash out a bunch at a time. Good to iron out the strategy first though with these simple PRs, saves work in the long run, well done.

[GideonBature]

For methods that return Null I don't think we need to add a type. We can just use an integration test to prove the return is null. If Core later changes the test will catch it. Then we change the 'Returns' column to 'returns nothing'.

For reference see submitblock in v17 (client and types).

Aright, Noted...

[GideonBature]

Once this is approved, I’ll proceed with the next one.

Once we have a few of these merged I'd say you'll have the idea and then you can just smash out a bunch at a time. Good to iron out the strategy first though with these simple PRs, saves work in the long run, well done.

True...

[tcharding]

Hey mate, when I merge PRs in this repo I use the Bitcoin Core merge script. And because of that if there are mentions (using @ character) they get included in the merge commit, then later github ends up spamming the mentioned dev everytime the merge commit shows up someplace (I don't know exactly where I just know I got spammed heaps in the past). So in this repo, and rust-bitcoin please don't put mentions in the PR description.

[tcharding]

Super happy with this man, the new return in v23 is exactly why this work is useful. Nice to have found success on the second try (after pruneblock).

[GideonBature]

Hey mate, when I merge PRs in this repo I use the Bitcoin Core merge script. And because of that if there are mentions (using @ character) they get included in the merge commit, then later github ends up spamming the mentioned dev everytime the merge commit shows up someplace (I don't know exactly where I just know I got spammed heaps in the past). So in this repo, and rust-bitcoin please don't put mentions in the PR description.

Alright. Sorry for that...

[tcharding]

No stress!

[tcharding]

Hey mate, if you think of it. When you force push can you post a quick message saying either what the force push is or what the status of the PR is. Otherwise I have to check out the branch, context switch into this PR, then work out if my last review suggestions were seen to etc - this all takes brain power, of which I only have a limited amount.

[tcharding]

ACK 565702f

[GideonBature]

Hey mate, if you think of it. When you force push can you post a quick message saying either what the force push is or what the status of the PR is. Otherwise I have to check out the branch, context switch into this PR, then work out if my last review suggestions were seen to etc - this all takes brain power, of which I only have a limited amount.

True, I will start doing that now...