What this PR does

This PR fixes two issues with the implementation of comparison operations between two vectors without the bool modifier in MQE:

• Queries would return incorrect results if the left side contained series with different metric names, and all results would be merged into a single series rather than returned in separate series for each metric name
• Queries would incorrectly fail with a conflict error if multiple series on the left side matched the same series on the right side, those left side series had points at the same timestamp, and one or none of those points remained after applying the comparison operation

This PR is a draft pending benchmarking and profiling of the impact of these changes.

Which issue(s) this PR fixes or relates to

#10067

Checklist

• Tests updated.
• [n/a] Documentation added.
• [covered by Mimir Query Engine #10067] CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• [n/a] about-versioning.md updated with experimental features.