refactor: convert LineZone docstring example to doctest

[vincenzonetti]

Before submitting

• Self-reviewed the code
• Updated documentation, follow Google-style
• Added docs entry for autogeneration (if new functions/classes)

Description

i converted static docstring examples to doctest format for the LineZones file

Type of Change

• 📝 Documentation update

Motivation and Context

Part of #2106

Additional note

It's actually my first PR on the project. I have only changed one file, but if the change happens to be correct, I could improve this PR by doing the conversion on more files.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77%. Comparing base (48035c1) to head (4468142).
⚠️ Report is 1 commits behind head on develop.

❌ Your project check has failed because the head coverage (77%) is below the target coverage (95%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #2207   +/-   ##
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  Coverage       77%     77%           
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  Files           62      62           
  Lines         7640    7640           
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  Hits          5919    5919           
  Misses        1721    1721           

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[Borda]

@vincenzonetti lets tkeep this pattern and in the docstring create trivial generators which created, for example, an empty file frames

[Copilot]

Pull request overview

This PR updates the LineZone class documentation by converting its docstring example into a doctest-friendly interactive session, supporting the repo-wide goal of continuously validating documentation examples.

Changes:

• Replaced the previous static Markdown example in LineZone’s docstring with a minimal >>>-style doctest example.

[Copilot]

Docstring examples elsewhere in the repo typically wrap >>> doctest sessions in a fenced Markdown block (e.g., pycon ... ). Consider adding a ```pycon fence around this example to keep documentation rendering and style consistent across the project.

[Copilot]

This doctest currently asserts (0, 0) after a single trigger() call, which doesn’t exercise the core behavior of counting a crossing (counts will remain zero even when inputs are valid). To make the doctest actually validate LineZone behavior, consider calling trigger() for the same tracker_id on two successive positions on opposite sides of the line and asserting that in_count or out_count increments.

Suggested change

	... xyxy=np.array([[10, 110, 20, 120]]),
	... tracker_id=np.array([1])
	... )
	>>> crossed_in, crossed_out = line_zone.trigger(detections)
	>>> line_zone.in_count, line_zone.out_count
	(0, 0)
	... xyxy=np.array([[10, 80, 20, 90]]),
	... tracker_id=np.array([1])
	... )
	>>> _ = line_zone.trigger(detections)
	>>> detections = sv.Detections(
	... xyxy=np.array([[10, 110, 20, 120]]),
	... tracker_id=np.array([1])
	... )
	>>> _ = line_zone.trigger(detections)
	>>> line_zone.in_count + line_zone.out_count
	1