Fix SummaryWriter writing to disk when write_to_disk=False in add_scalars (#748)

[lanpa]

This PR fixes issue #748 where SummaryWriter continued to write to disk even when write_to_disk=False was specified. The bug was in the add_scalars method, which directly instantiated a FileWriter instead of checking the flag. I have also added a regression test in tests/test_writer.py.\n\nAI assisted

[lanpa]

@copilot review this PR

[Copilot]

@copilot review this PR

The fix in commit 2b76fac looks correct. Here's a summary of the review:

What was changed:

• add_scalars in writer.py previously always created a FileWriter for each scalar tag, bypassing the write_to_disk flag entirely. The fix checks self._write_to_disk and creates a DummyFileWriter instead when it's False.
• The fix also correctly passes max_queue, flush_secs, and filename_suffix to FileWriter (previously these were not forwarded, so add_scalars would have used defaults even when write_to_disk=True).
• A regression test test_write_to_disk_false is added that covers both add_scalar and add_scalars.

One observation (pre-existing, not introduced by this PR):
The _get_file_writer() method (line 372–374) recreates the DummyFileWriter and resets all_writers on every call when _write_to_disk=False. This is harmless since DummyFileWriter is a no-op, but it means all_writers can grow with add_scalars tags and then get replaced on the next _get_file_writer() call. Not a bug, but worth knowing.

Overall the fix is minimal, targeted, and correct.