Export of larger data sets are slow with no indicator

[tylerkron]

If you have a decent number of data points, export takes a while and there is no progress indicator.

Steps to reproduce

1. Enable 5 channels
2. Set frequency to 500Hz
3. Stream for 60 seconds
4. Export and notice that it takes minutes to actually create the export

Success Criteria

• Large dataset exports should not exceed a 30-second processing time.
• A visible progress indicator (e.g., progress bar or spinner) must display during the export process.
• The user must have an option to cancel the export process at any time.