feat(graphql): add metrics top-level query and questTimelineChart (#2126)

Adds a `metrics` top-level GraphQL query resolving `questTimelineChart` for use in dashboard UI.
It fetches quests, buckets them into discrete time intervals based on a `granularity_seconds` parameter, and groups the items inside each bucket by their executing Tome's tactic. Empty buckets are preserved and padded with zero counts to maintain uniform timeline chart data.

Also includes unit tests covering precise interval generation and empty bucket edge cases.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: KCarretto <16250309+KCarretto@users.noreply.github.com>

Author: KCarretto