Convert overflow Serializing DateTime64 < epoch to Protobuf

### Company or project name

ClickHouse

### Describe what's wrong

Attempting to serialize a DateTime64 prior to 1970-01-01 to Protobuf throws a Convert overflow error.

### Does it reproduce on the most recent release?

Yes

### How to reproduce

```
:) INSERT INTO FUNCTION file('test.tmp', 'Protobuf', 't DateTime64(6)') SETTINGS date_time_output_format='iso', engine_file_truncate_on_insert=1 FORMAT TSV
1969-01-01 00:00:00+00

Received exception:
Code: 407. DB::Exception: Convert overflow. (DECIMAL_OVERFLOW)

:) INSERT INTO FUNCTION file('test.tmp', 'Protobuf', 't DateTime64(6)') SETTINGS date_time_output_format='iso', engine_file_truncate_on_insert=1 FORMAT TSV
1970-01-01 00:00:00+00

Ok.

```

### Expected behavior

I would think that the Protobuf Timestamp type can handle dates before the epoch. If not, perhaps refuse to attempt to serialize if the timestamp is out of range.

### Error message and/or stacktrace

Code: 407. DB::Exception: Convert overflow. (DECIMAL_OVERFLOW)

### Related issues and pull requests

_No response_

### Additional context

_No response_

Start by running the supplied INSERT statements against the Protobuf file output path and compare the pre-epoch and epoch results. Trace the DateTime64-to-Protobuf Timestamp conversion involved in that path; done means dates before 1970 serialize successfully, or out-of-range values are rejected with a clear, intentional error.

Written by the indexing model from the issue text.