refactor(rust): make it easier to write commands' api req/res handlers

[adrianbenavides]

Add an abstraction layer on top of connect_to to make it easier to write commands' api req/res handlers. It removes a lot of boilerplate around calling the background node and especially, around handling errors. This can prove especially helpful for new contributors.

[mrinalwadhwa]

@adrianbenavides I really like where you're going with this PR 👍

[adrianbenavides]

+1 Looks good to me! I just left some minor suggestions.

Thanks for all the comments! I've fixed all you pointed out in my last commit.

[mrinalwadhwa]

@Mergifyio refresh

[mergify[bot]]

refresh

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