replace tqdm and async progress with richpool (resolves #76)

[sahiljhawar]

Replace multiprocessing.Pool and manual tqdm-polling with richpool

Swaps every Pool/map_async + manual tqdm-polling progress bar for richpool.p_map (parallel) or richpool.t_map/make_progress (sequential) across interp_functions.py, bin_and_interpolate_to_model_grid.py, and magnetic_field_functions.py. Removes the now-dead show_process_bar_for_map_async helper and its unreachable isinstance(result, Exception) checks. worker exceptions already propagate through p_map the same way they did through Pool.map_async(...).get(). Adds richpool as a dependency in pyproject.toml.

Resolves #76.

[DoctorRabbit55]

Thanks, Sahil! Can you please verify that this is equally fast as before? I had bad experiences with p_tqdm regarding speed in the past

[sahiljhawar]

I have checked locally. the speed change is negligible.

[DoctorRabbit55]

I think this is a better way to generate the progress bar for parallel tasks, but I would rather keep tqdm for simple for loops, as it does not require wrapping your loop into a function.

[sahiljhawar]

just want to make it consistent :)