Check for point source release

[smaticka]

Some plotting near the coasts shows up all gray when using cdr_forcing.plot_distribution(). When the release will be treated as a point source in ROMS, it causes issues when trying to visualize. Two issues are addressed and changed as follows:

Currently, RT considers cells with > 1e-3 a fraction of the total. If the all cell fractions are < 1e-3, the integral of the field sums to 0. This results in a distribution of all nans (when all values are normalized by the integral - in this case, divided by 0). This PR checks if any cells have fraction > 1e-3, if none, then the release is treated as a point source.

If hsc (horizont scaling for the gaussian) is too low, the function fcn = np.exp(-((dist / hsc)^2)) evaluates to 0. for values of dist/hsc >=28 fcn evaluates to 0 in python. A check is added to treat cases like this as a point source.

• Closes Plotting CDR release near coast shows blank #435
• Passes pre-commit run --all-files
• Changes are documented in docs/releases.md

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.39%. Comparing base (fcc9a32) to head (ea2b2cb).

Files with missing lines	Patch %	Lines
roms_tools/setup/cdr_forcing.py	50.00%	4 Missing and 2 partials ⚠️

@@            Coverage Diff             @@
##             main     #600      +/-   ##
==========================================
- Coverage   89.47%   89.39%   -0.08%     
==========================================
  Files          28       28              
  Lines        6130     6141      +11     
  Branches     1093     1096       +3     
==========================================
+ Hits         5485     5490       +5     
- Misses        365      369       +4     
- Partials      280      282       +2     

Flag	Coverage Δ
glorys-regional-invariance	36.15% <0.00%> (-0.07%)	⬇️
with-dask-1	80.32% <0.00%> (-0.15%)	⬇️
with-dask-2	51.81% <0.00%> (-0.10%)	⬇️
with-dask-and-xesmf-1	85.01% <50.00%> (-0.08%)	⬇️
with-dask-and-xesmf-2	55.31% <0.00%> (-0.10%)	⬇️
without-dask	84.04% <0.00%> (-0.16%)	⬇️

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Files with missing lines	Coverage Δ
roms_tools/setup/cdr_forcing.py	87.53% <50.00%> (-1.19%)	⬇️

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