Fix(clickhouse): use DateTime64(6) type in incremental time filter

[treysp]

Clickhouse background

Clickhouse has two datetime types:

• DateTime: fixed one second precision
• DateTime64: user-specified precision (default of 3/millisecond when bare type passed)

Clickhouse errors if you try to cast a string containing fractional seconds to DateTime.

Current PR

SQLMesh time intervals are sometimes calculated as [datetime - 1 microsecond], returning values containing fractional seconds.

This PR prevents fractional second casting errors by always using DateTime64 in incremental time filters. It uses a default precision of 6 unless the user explicitly passed DateTime64.

The returned type is non-nullable by default. In SCD models, however, we generate statements like CAST(NULL AS DateTime64) that require a nullable type. Therefore, we force nullable types when calling to_time_column() in the SCD adapter method.

[erindru]

LGTM, were you meant to leave this as Draft?

[treysp]

I thought this could be affected by how we go in tobymao/sqlglot#4269, so was holding it until that is resolved