[PLAT-377] add cast operator support in metrics sql, also enable "cast_string_to_date_time_mode" for clickhouse

[pjain1]

CH does not support automatically converting zulu formatted time 2025-12-25T00:00:00Z to DateTime. A config cast_string_to_date_time_mode enables this but still needs a cast to be added to the string typed time value.

This fix adds support for CAST operator in metrics_sql but only for DateTime and Timestamp type. This will enables api users to pass in datetime as string with the condition that they cast the param in api like day >= CAST('{{ .args.startDate }}' AS DateTime). This also supports Rill time functions so this is also supported day > CAST(time_range_start('P30D') AS DateTime).

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]

Tests failing because test CH is old version not supporting this config added in 25.6.

[begelundmuller]

1. Unsafe type cast – can we make it safe? (Just to protect against panics)
2. Since SQL types differ between different OLAPs, can we use a generic type here that is not DB-specific? Maybe accept a runtimev1.Type_Code and use drivers.Dialect to map it to a SQL type for common types (can just handle timestamps for now)?

[pjain1]

Using runtimev1.Type and also added a test.

Also not setting cast_string_to_date_time_mode in the code by default because we have check for min supported version of 22.7 and this config is available in 25.6. We can set it through connector.clickhouse.query_settings="cast_string_to_date_time_mode='best_effort'" for projects needing this.