Add set sequence adaptors

[jnytra]

Add the following set sequence adaptors that operate on sorted sequences:

• set_union - computes the union of two sets
• set_difference - computes the difference between two sets
• set_symmetric_difference - computes the symmetric difference between two sets
• set_intersection- computes the intersection of two sets

Closes #72

[jnytra]

I wrote my first adaptor (set_union). @tcbrindle, if you have time to take a look at my code, I'd be happy for feedback. Then I could continue on the other set adaptors. I apologize for not creating the issue ahead of time. Hopefully you haven't worked on this adaptor already.

[tcbrindle]

Sounds good! Don't worry, I haven't been working on these :)

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (1c0dc6e) 97.85% compared to head (7d21175) 97.85%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #73 +/- ## ======================================= Coverage 97.85% 97.85% ======================================= Files 65 65 Lines 2191 2191 ======================================= Hits 2144 2144 Misses 47 47 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.

[jnytra]

Thank you very much for your review. I think it has pushed me a lot and I hope I won't make so many mistakes in the future.

[tcbrindle]

Thank you very much for your review. I think it has pushed me a lot and I hope I won't make so many mistakes in the future.

You're not making mistakes :) This stuff is really tricky and most of the information about how it works only exists in my head at the moment, so you've done an amazing job. Also I'm probably being more fussy than usual about style things because Flux is my "baby" and I want it all to be perfect!

[tcbrindle]

I was going through looking at the updated version but I see you're still making changes, so please let me know when it's ready for review again :)

[jnytra]

For now I am done. If you want you can look at it.

[jnytra]

I hope I have corrected all the comments. Thank you for them.

[jnytra]

I added the remaining set adaptors. If you have time, you can take a look at it. @tcbrindle

[tcbrindle]

Looks like my changes in #76 and #77 have broken things, sorry!

[jnytra]

No problem. I will try to fix it.

[jnytra]

Thanks much for review! I hope that I fixed all comments. I am not sure, why Codecov job failed. It seems that I cannot retry it. Also, I do not know how to check if documentation render correctly.

[tcbrindle]

Thanks much for review! I hope that I fixed all comments. I am not sure, why Codecov job failed. It seems that I cannot retry it. Also, I do not know how to check if documentation render correctly.

I've fixed CodeCov in #81 (lcov was updated from 1.16 to 2.0 which broke the our Github Actions script).

Please could you merge the latest upstream changes and try again? Github will allow me to do it, but updating someone else's repository feels a bit rude!

[jnytra]

The latest upstream changes merged. Now all jobs passed.

[tcbrindle]

Sorry it's taken me a few days to get to this, it's a lot of code to look through! But it all looks really great. Not just one but four tricky adaptors, you've done a great job!

[jnytra]

Nothing happens, I was on vacation anyway. Thank you very much for the review.