Is your feature request related to a problem? Please describe.

When fetching timestamp values, the tabledata.list and jobs.getQueryResults APIs return a floating point value by default.

This can cause unexpected floating point issues when rounding timestamps in SQL, such as with the TIMESTAMP_TRUNC(COL_TIMESTAMP, MILLISECOND) function.

Describe the solution you'd like

The backend API adds a formatOptions.useInt64Timestamp option.

• Wherever tabledata.list, jobs.query, or jobs.getQueryResults are called, set the formatOptions.useInt64Timestamp option to True.
• Wherever timestamps in rows API responses are handled, update it to use integer math to extract microseconds and seconds.
• Add system tests to verify that timestamps rounded to every digit of supported precision (e.g. 9, 9.9, 9.99, ..., 9.999999) are returned exactly as set in the table/query.

Describe alternatives you've considered

N/A

Additional context

Precision issues for the other direction (to BigQuery) for similar floating-point reasons: #392