fix(bluebubbles): raise send_file timeout to cover slow uploads (#77918)

[webtecnica]

Summary

Fixes #77918. The BlueBubbles attachment upload in _send_attachment used a hardcoded timeout=120, but on macOS 26 a successful attachment send routinely takes ~2 minutes to return. The client-side timeout fired first, _send_attachment returned SendResult(success=False), and the user saw "Couldn't deliver the file attachment" moments after the file actually arrived.

Root Cause

gateway/platforms/bluebubbles.py posted to /api/v1/message/attachment with timeout=120, well below BlueBubbles Server's own internal upload timeout of 300s. The gateway log showed the failure warning exactly 120s after the send started, even though delivery succeeded.

Change

• Added a class constant BlueBubblesAdapter.ATTACHMENT_UPLOAD_TIMEOUT = 300, matching BlueBubbles Server's own 300s internal limit, and used it for the attachment upload request instead of the hardcoded 120s.

Verification

• New test TestBlueBubblesAttachmentUpload::test_send_attachment_uses_300s_upload_timeout asserts _send_attachment posts to /api/v1/message/attachment with timeout == 300 and returns success.
• Full BlueBubbles test file: 19 passed.

Closes #77918