fix(bigquery): align DATE() function output to TIMESTAMP for SQL API compatibility

[tlangton3]

Summary

Fixes #10643. When querying via the SQL API (Postgres wire protocol), CAST(x AS DATE) = DATE('2024-01-08') generates TIMESTAMP = DATE on BigQuery, which BigQuery rejects. This pattern originates from Tableau connecting via the SQL API.

Changes

• Override the functions/DATE template for BigQuery to produce TIMESTAMP(args) instead of DATE(args), aligning the SQL output with the date UDF's declared Timestamp return type in CubeSQL
• Add CAST(? AS TIMESTAMP) for time dimension filter parameters in BigqueryFilter.castParameter() (defence-in-depth for the standard filter code path)
• Add an integration test covering the MEASURE() query shape with CAST(x AS DATE) = DATE('...')
• Add an MSSQL skip for the new test (MSSQL has no DATE() builtin)

Implementation Details

The CubeSQL date UDF declares its return type as Timestamp for compatibility with the egg rewrite engine's time dimension filter patterns. However, the functions/DATE SQL template in BaseQuery.js renders as DATE(args) which produces a DATE type in BigQuery. When plan_normalize coerces the other side of a comparison to match the Timestamp return type, the generated SQL becomes TIMESTAMP = DATE — which BigQuery rejects.

The fix overrides the DATE function template for BigQuery to produce TIMESTAMP(args). This is safe because the hardcoded DATE() calls in time series templates (e.g. GENERATE_DATE_ARRAY(DATE(...))) are inline strings within those templates, not calls to the functions/DATE template. Templates are shared between the JS Cube server and Rust wrapper.rs, so a single override covers both SQL generation paths.

The castParameter change is an additional safety net for cases where time dimension filter parameters reach BaseFilter.equalsWhere() directly.

Testing

• All 699 CubeSQL Rust unit tests pass (no Rust changes required)
• BigQuery integration tests with Tesseract ON: 96 passed, 2 failed (pre-existing — `SQL API: ungrouped pre-agg` snapshot ordering and `Tesseract: SQL API: Timeshift measure from cube` Timestamp+Interval coercion), 38 skipped — no regressions
• New integration test `SQL API: Date/time comparison with DATE() function in SQL push down` verifies the fix end-to-end against live BigQuery

Notes for reviewers

• The new integration test will need a snapshot regenerated (`jest --updateSnapshot`) for non-BigQuery drivers (Postgres, MySQL) on first CI run — the query itself returns deterministic data across drivers
• An earlier draft of this PR included a duplicative COUNT+GROUP BY test, removed in the final commit because both query shapes exercise the same `push_to_cube=true` (JS) path; the template fix benefits all paths via shared template definitions

Linear Ticket

N/A