Allow GROUP BY queries by providing deserialize_next_tagged to deserialize the group fields

[SafariMonkey]

Description

This change adds deserialisation for the metadata of a GROUP BY using the method deserialize_next_tagged, which takes a TAG parameter (so called because that's what the InfluxDB response calls it) which is deserialized from the metadata. Because Series has a custom deserializer, this means TaggedSeries also has to. It's pretty copy paste, with minimal code changes, and leverages the existing Series value deserialisation. I originally tried to abstract over having tags and not but it ended up being way hairier and more error prone, so I thought copying ~100 lines of boilerplate is probably fine.

I've tested this on my code and it works fine. I also added a test and that passes.

Side note, is the #[doc(hidden)] something that can be removed? The user has to use that struct to access the series.

Checklist

• Formatted code using cargo fmt --all
• Linted code using clippy cargo clippy --all-targets --all-features -- -D warnings
• Updated README.md using cargo readme -r influxdb -t ../README.tpl > README.md
• Reviewed the diff. Did you leave any print statements or unnecessary comments?
• Any unfinished work that warrants a separate issue captured in an issue with a TODO code comment

[Empty2k12]

Hey @SafariMonkey, sorry for my absence. I tested this PR and it's working beautifully. Thanks for the work!

Side note, is the #[doc(hidden)] something that can be removed? The user has to use that struct to access the series.

In the past, it was not needed, so that's why the #[doc(hidden)] was added. If it's public, maybe a better name for TaggedReturn can be chosen, or do you think it's okay to keep it like that?

[cryptoquick]

A rose by any other name would still smell as sweet. I suggest merging this, and if there's additional aesthetic clarity, it can come in via another pull request.

[SafariMonkey]

I'm fine with @cryptoquick's suggestion. If you want to change the name feel free, but I'm happy enough with it as is. I already gave it a once over before submitting it.

[Empty2k12]

Thanks for your second awesome contribution!

[cryptoquick]

@SafariMonkey yes, thanks for working on this even though it's no longer core to your project. And thank you, @Empty2k12 for being such a responsive maintainer, even over the weekend! Rust is a healthier community thanks to both of your efforts.

[Empty2k12]

I will release a build on crates.io today or tomorrow. Thanks again.

[SafariMonkey]

@cryptoquick As a slight correction, I was only saying before that writing to InfluxDB wouldn't be able to be handled by this library due to its quoting - the reading is still this library. It's only a prototype I'm putting together during some spare moments, hence the long silence last month.

I'm happy that these PRs can help the project, and I will continue to submit them should I run into areas that I think could use improvement.

I'd also like to echo the appreciation for your work in reviewing these changes and your responsiveness, @Empty2k12. And it's nice to have a PR so well received :)

[Empty2k12]

@SafariMonkey @cryptoquick Sorry for the long wait, but the v0.2.0 version is now live on crates.io.