Use reactions for confirmation when appropriate

[isomorpheme]

Closes #198. This ended up being more work than you'd expect, and due to a seeming omission from GitHub's API, we can't send a reaction in every case, in which case we fall back to an old-fashioned comments. I also decided to fall back to posting a comment if the PR isn't immediately at the top of the merge queue, but maybe there's no need to be that informative.

Depends on haskell-github/github#509 to be able to use the Reactions API. I've added that as a patch to the Nix overlay; if there's contributors that want to work without Nix then it should be doable to get that patch by adding to cabal.project as well.

[isomorpheme]

Example of my local hoff using reactions: isomorpheme/sandbox#2

[rlycx]

source code itself looks good, but could you add a test case for this (or point me to something that tests this particular feature if i overlooked it)?

[isomorpheme]

could you add a test case for this (or point me to something that tests this particular feature if i overlooked it)?

I already added test cases here: https://github.com/channable/hoff/pull/272/files#diff-5057de5eb61e3ca52c8f206f6964e0486e9257418d5d39ab89f3cfaaf6e97839R913-R992

Very understandable if you missed that though, the diff is unfortunately large & has a lot of repetition.

[rlycx]

neat! thank you :3

[isomorpheme]

@OpsBotPrime merge

[OpsBotPrime]

Pull request approved for merge by @isomorpheme, waiting for rebase behind one pull request.

[OpsBotPrime]

Speculatively rebased as 30575d7 behind 1 other PR, waiting for CI …

[OpsBotPrime]

CI job 🟡 started.