More accurately type ActiveRecordRelations calculation methods

[jeffcarbs]

Motivation

Currently the calculation methods like sum and count return T.untyped. For some methods we cannot know the type (e.g. minimum) but for others we at least know it's numeric (e.g. sum) and for count we know it's an Integer.

However, I'm assuming these are untyped because if they're used with group the return value is actually a hash where the keys cannot be typed but the values will be the types mentioned above. This PR updates the ActiveRecordRelations compiler to type these correctly.

Implementation

I first updated the return values of the calculation methods where possible. Then I largely copied from the code around PrivateRelationWhereChain to add a PrivateRelationGroupChain module which defines the calculation methods with the hash return values.

Some callouts:

• Unlike "WhereChain", there's no such analogous GroupChain runtime class available so this is solely made for RBI. From looking at the source it looks like when a query uses group some metadata is added to it.
• Technically a group anywhere in the query chain produces this behavior but to avoid needing to re-type every query method inside this module we make a simplifying assumption that the calculation method is called immediately after the group (e.g. group().count and not group().where().count). The one exception is group().having().count which is fairly idiomatic so that gets handled without breaking the chain.

Tests

Updated the existing specs.

[KaanOzkan]

@jeffcarbs sorry for the wait looks like the review automation failed. Could you rebase on main? Thanks.

[jeffcarbs]

@KaanOzkan - rebased and pushed up a new build.

[jeffcarbs]

I think you need to add a label, enhancement probably makes the most sense. I would add it but I don't think I have permission.

Also it looks like the build are failing on main:

[KaanOzkan]

Thanks I'll now take a look. And yes the build failures seem to be because we remove Gemfile.lock and bump google-protobuf during CI #1819

[KaanOzkan]

This LGTM from my limited understanding of group and calculation methods. Tested on a small Rails app as well.