fix(cubesql): Generate typed null literals #3640

Job	Run time
latest-tag-sha	22s
Build native Linux 20 x86_64-unknown-linux-gnu Python fallback	2m 50s
build	6m 48s
tests (20.x, athena-export-bucket-s3)	18m 28s
tests (20.x, bigquery-export-bucket-gcs)	9m 11s
tests (20.x, clickhouse)	5m 24s
tests (20.x, clickhouse-export-bucket-s3)	6m 3s
tests (20.x, databricks-jdbc)	6m 38s
tests (20.x, databricks-jdbc-export-bucket-s3)	6m 33s
tests (20.x, databricks-jdbc-export-bucket-azure)	6m 24s
tests (20.x, mssql)	5m 32s
tests (20.x, mysql)	5m 16s
tests (20.x, postgres)	5m 12s
tests (20.x, redshift)	5m 24s
tests (20.x, redshift-export-bucket-s3)	6m 45s
tests (20.x, snowflake)	5m 48s
tests (20.x, snowflake-export-bucket-s3)	5m 44s
tests (20.x, snowflake-export-bucket-azure)	5m 48s
tests (20.x, snowflake-export-bucket-azure-via-storage-integration)	5m 48s
tests (20.x, snowflake-export-bucket-gcs)	5m 45s
	2h 5m 43s

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