[PLAT-440] roll up routing in metrics view

[pjain1]

• Add rollup table config to metrics view proto and YAML parser
• Implement query routing: eligible rollups are selected based on grain derivability, dimension/measure coverage, timezone match, time range alignment, and time coverage
• Prefer coarsest grain among eligible rollups; break ties by smallest data range
• For no-time-range queries ("all data"), verify the rollup covers the base table's full range rather than skipping coverage checks

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[pjain1]

Instead of directly querying for watermarks here, I explored using metrics_time_range resolver approach so that we can rely on user defined cache_key_ttl and cache_key_sql to not fetch watermark until needed. It also helps with automatically invalidating cache if rollups are Rill managed as the resolver cache key will rely on metrics view status updated on.

However, the only issue I see is for external olap (majority of cases), mv cache is disabled by default so resolver ends up querying watermarks for all eligible rollups for every single query (contrast with current behaviour where time range is only queried once for time picker). In this case I was thinking of an L1 cache having simple time based ttl of lets say 1 or 5 minutes in this file and only if that expires then call metrics_time_range resolver. I already have the changes locally if needed. Thoughts?