fix: pl.show() now displays in a plain Python REPL (#68)

[timtreis]

Problem

Fixes #68. pl.show() did not display the figure in a plain Python REPL (PyCharm console, pasted REPL, python -i); users had to call plt.show() manually. Most recently re-reported here.

Root cause

The show=None default keyed off not hasattr(sys, "ps1"). A plain Python REPL sets sys.ps1 but leaves matplotlib non-interactive (unlike Jupyter/IPython), so plt.show() was suppressed and nothing rendered.

Fix

Drop the sys.ps1 check and decide purely on matplotlib.is_interactive():

• interactive backends (Jupyter, IPython, plt.ion()) auto-render → no plt.show();
• scripts and plain REPLs are non-interactive → explicit plt.show().

The new condition is strictly more permissive than the old one, so it never suppresses a show() the old code emitted — it only adds the missing REPL case. Removed the now-unused import sys.

Tests

Added test_show_default_keys_off_is_interactive (parametrized over the interactive flag, sys.ps1 set in both cases to prove the decision ignores it). Verified to fail on the old logic and pass on the fix.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.59%. Comparing base (227434d) to head (364416f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #745      +/-   ##
==========================================
- Coverage   79.59%   79.59%   -0.01%     
==========================================
  Files          17       17              
  Lines        4641     4640       -1     
  Branches     1029     1029              
==========================================
- Hits         3694     3693       -1     
  Misses        598      598              
  Partials      349      349              

Files with missing lines	Coverage Δ
src/spatialdata_plot/pl/basic.py	82.78% <100.00%> (-0.04%)	⬇️

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