Add --rune flag to resume command to enable resuming a specific etching

[ldiego08]

Adds a new --rune <RUNE> flag to allow resuming a specific pending etching. This is useful in automated scenarios (if anyone else is into that kind of stuff) where you'd like to etch something, suspend (perhaps via --no-wait from #3526), do something else, and then resume after the 6 confirmations.

[ldiego08]

Thanks for the feedback, @raphjaph! Requested changes have been applied. I've also fixed linting issues. Will add the command to show pending etchings on a separate PR.

[ldiego08]

Almost there! Still needs an integration test. Have a look at tests/wallet/resume.rs. For reasons this can only be tested on Mac and Linux. What system are you on?

@raphjaph took me a while to get around to adding these tests, but here they are! Hope it's looking good. I'm on a Mac, btw.