chore(blooms): Some boom gateway cleanups

[chaudum]

What this PR does / why we need it:

• Cleanup logic for processing multiple days
  in single FilterChunkRefs request in the bloom gateway. The handler
  already returned an error if the requested chunk refs spanned across
  multiple days, but the logic for processing multiple days/tasks was
  still in place. This commit simplifies the logic to only process a
  single task per request.

• Remove unused package global variable

• Remove bloomgateway package comment

• Remove duplicate imports

• Avoid conversion from *logproto.ShortRef to v1.ChunkRef
  and istead cast the value of the pointer

• Simplify getFromThrough() function

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[vlad-diachenko]

I have not found any issues ;) LGTM