astrocalc: issue warning for potential overload

[axd1967]

Is your feature request related to a problem? Please describe.
The user might make mistakes when choosing the start and end date/times, in combination with very small time steps.
Example: specifying 2021-01-12 to 2023-01-12 with a time step of 1 minute.

Describe the solution you'd like

One or more of

• Show a confirmation panel when the calculations would require more than N results, where N is to be either a user configurable value (via dialog and/or config.ini). include the computed number of rows that would be generated.
• show the expected number of steps as a fixed field in the astrocal dialog; highlight that field when it exceeds N
• Update the progress bar to give an indication how far the calculations are. A very nice solution could be to use the "Execute" button to show the progress bar; but there is already a progress bar mechanism available in Stellarium.
• Provide a user-friendly means to cancel/interrupt long-running calculations

This is a simple example how to guard the user against silly mistakes.

Describe alternatives you've considered
None. Stellarium must be killed in order to stop the computations.

Additional context

[10110111]

I have been caught by this a few times too. Best UX would be to have all of the following:

1. responsive UI during calculations (e.g. move calculations to a separate thread),
2. progress indication,
3. a cancel button (this requires item 1, responsivity).

[github-actions]

Hello @axd1967!

Thank you for suggesting this feature.