Add layout option to coda plot_boxplots (#718)

[emekaokoli19]

PR Checklist

• Referenced issue is linked
• If you've fixed a bug or added code that should be tested, add tests
• Documentation in docs is updated

---

Description of changes

This PR adds a new layout parameter to plot_boxplots() in the Sccoda plotting utilities.

Currently, when plot_facets=True, the number of subplot columns is determined using:

col_wrap = int(np.floor(np.sqrt(K)))

where K is the number of cell types. This tends to produce a taller ("long") layout for the facet grid.

The new layout parameter allows users to choose between two layouts:

• "long" (default): uses floor(sqrt(K)), producing a taller layout.
• "wide": uses ceil(sqrt(K)), producing a wider layout.

Example usage:

sccoda.plot_boxplots(
    mdata,
    feature_name="condition",
    plot_facets=True,
    layout="wide"
)

The default behavior remains unchanged to preserve backward compatibility.

This resolves #718.

---

Technical details

When plot_facets=True, the column wrapping logic now depends on the layout argument:

• "long" → col_wrap = floor(sqrt(K))
• "wide" → col_wrap = ceil(sqrt(K))

Validation is added to ensure layout is either "long" or "wide".

The change only affects the FacetGrid layout logic and does not impact any other functionality.

---

Additional context

This change improves flexibility for users visualizing many cell types, where a wider layout may be preferable for readability.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.94%. Comparing base (12897e1) to head (41155c6).
⚠️ Report is 41 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #932      +/-   ##
==========================================
- Coverage   73.54%   71.94%   -1.60%     
==========================================
  Files          48       48              
  Lines        5613     5746     +133     
==========================================
+ Hits         4128     4134       +6     
- Misses       1485     1612     +127     

Files with missing lines	Coverage Δ
pertpy/tools/_cinemaot.py	59.23% <100.00%> (ø)
pertpy/tools/_coda/_base_coda.py	57.64% <100.00%> (+0.47%)	⬆️
pertpy/tools/_coda/_tasccoda.py	72.90% <100.00%> (ø)
pertpy/tools/_milo.py	63.50% <100.00%> (-17.16%)	⬇️

... and 7 files with indirect coverage changes

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