Fix pandas-compatible scalar assignment in tdating

[dnerini]

This PR fixes pysteps.tracking.tdating DataFrame assignments to use scalar-safe .at[...] when storing array/list-like values (prevents pandas length-mismatch errors in output_splits_merges=True multistep tracking).

additionally:

• Fix Python 3.13 SyntaxWarning: invalid escape sequence warnings in docstrings/labels (nowcasts.interface, timeseries.correlation, fit_vel_pert_params.py).
• Reduce IO-related warning noise by:
  • explicitly setting GDAL exception mode (DontUseExceptions) in IO importer/exporter modules
  • avoiding NumPy 2.x deprecation warnings in SAF CRRI netCDF reads (np.asarray(...[:])).

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.85%. Comparing base (a6a6e5b) to head (9d2ff54).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
pysteps/scripts/fit_vel_pert_params.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #539      +/-   ##
==========================================
+ Coverage   83.84%   83.85%   +0.01%     
==========================================
  Files         168      168              
  Lines       14630    14634       +4     
==========================================
+ Hits        12267    12272       +5     
+ Misses       2363     2362       -1     

Flag	Coverage Δ
unit_tests	83.85% <92.00%> (+0.01%)	⬆️

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[RubenImhoff]

Fantastic, many thanks for this, @dnerini! Looks like the new pandas version gave some breaking changes.. Happy that this is resolved.