Mimir query engine: finish reorganisation started in #8230

[charleskorn]

What this PR does

This PR completes the reorganisation started in #8230.

In particular:

• The Operator interfaces and RingBuffer type have moved to the types package
• The operator package has been renamed to operators

This structure avoids circular dependencies between packages while allowing the pooling types to live in the pooling package, which allows us to protect the underlying pools from direct access.

I don't love the package name types, open to other suggestions.

Which issue(s) this PR fixes or relates to

#8230

Checklist

• Tests updated.
• [n/a] Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• [n/a] about-versioning.md updated with experimental features.

[jhesketh]

nice work, lgtm.

Re the types package, we could have a buffer package and then move the operator+data into streamingpromql?
Either that, or keep operator in the operators package, as I think that makes sense still.

[charleskorn]

Re the types package, we could have a buffer package and then move the operator+data into streamingpromql?

The data structures (eg. InstantVectorSeriesData) are the problematic ones - they're used both by the streamingpromql package and the operators package, so they either have to live in the operators package, or a third package. Otherwise, we'll create a circular dependency.

[charleskorn]

Given the approval, I'm going to merge - we can always change the name or organisation again if we think of a better way to do it.