Timestamps reported in change records values are incorrect

We're using change streams to observe changes to a table, which has two `TIMESTAMP` columns: `resource_version` and `previous_resource_version`.

`resource_version` is always updated with `PENDING_COMMIT_TIMESTAMP()` (which has [microseconds precision](https://cloud.google.com/spanner/docs/commit-timestamp#:~:text=Spanner%20commit%20timestamps%20have%20microsecond%20granularity%2Cand%20they%20are%20converted%20to%20nanoseconds%20when%20stored%20in%20TIMESTAMP%20columns.)), while `previous_resource_version` is updated with computed value.

After modifying the entry we can see following values in the table:

```
+--------------+----------------------------+-----------------------------+
| value | resource_version | previous_resource_version |
+--------------+----------------------------+-----------------------------+
| bmV3LXZhbHVl | 2025-02-19T13:55:36.43168Z | 2025-02-19T13:55:36.429694Z |
+--------------+----------------------------+-----------------------------+
```

However change record with this modification contains following "NEW" values:

```json
{
"previous_resource_version": "2025-02-19T13:55:36Z",
"resource_version": "9999-12-31T23:59:59Z",
"value": "bmV3LXZhbHVl"
}
```

There are two problems with this change record modification:
* `resource_version` column seem to contain placeholder value, instead of final value of `PENDING_COMMIT_TIMESTAMP()`.
* Both `resource_version` and `previous_resource_version` are reported with seconds precision, [instead of nanoseconds](https://cloud.google.com/spanner/docs/reference/standard-sql/data-types#timestamp_type).

When running the same code against cloud Spanner instance, we're seeing correct values in the change record (i.e. final value of commit timestamp and timestamps with microseconds).