fix: rilltime syntax in comparison time range in citation urls

[AdityaHegde]

LLM can use rill time for relative time ranges. Since backend supports it in comparison time range as well, it can use it in comparison as well. But UI doesnt support rill time, leading to removal of comparison all together.

Since watermark history at the time of query is not available, we are opting to resolve the time ranges and store it in the tool result.

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!