Add type annotations for metric

[harahu]

📚 Context

Continuing from where I left off in #4657

• What kind of change does this PR introduce?

  • Other, please describe: Type Annotations

🧠 Description of Changes

• Add type annotations for the metric module

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[vdonato]

LGTM --

We're technically barred from removing the str cast for the return type of st.metric now for backwards compatibility reasons. On the other hand I'd be shocked if someone were actually relying on the current st.metric return value, so we may be able to bend the rules here a bit and change its return type.

I'd prefer doing this because I just can't see how the current behavior is intentional / how anyone could possibly be relying on it.

[harahu]

I'd prefer doing this because I just can't see how the current behavior is intentional / how anyone could possibly be relying on it.

Due to the tiny, but still existent, chance that this might be intentional, I suggest merging this PR as is, and I can make a follow-up pretty rapidly that changes the return type to DeltaGenerator. I prefer doing it that way since it allows for easily reverting the breaking change, should it turn out controversial. It also allows discussing it with other parties before merge, without holding up the types.

[vdonato]

Due to the tiny, but still existent, chance that this might be intentional, I suggest merging this PR as is

Seems reasonable to me! I'll go ahead and merge this now.

I double-checked the (internal) spec that we wrote for this and couldn't find any mention of the return value for st.metric being any different from other non-widget elements. That paired with the fact that I can't see how a user would possibly want this behavior makes me lean toward believing that the current return value is simply an error. I'm happy to take the change correcting this return value on 🙂

[harahu]

I'm happy to take the change correcting this return value on 🙂

I'm more than happy to leave it to you, if you want to take it on. I appreciate the thorough follow-up!