FIX: Error with AxisItem.set_active & Curve Artifacts Remaining on Previous Axis

[YektaY]

Description

This PR addressed two errors.

1. In AxisItem.set_active, check that children widgets are CurveItems
2. When CurveItems are moved to a new AxisItem, the curve's error bar & extension line remained on the previous axis

Pre-merge checklist

• Code works interactively
• Code contains descriptive docstrings
• New/changed functions and methods are covered in the test suite where possible
• Test suite passes locally
• Test suite passes on GitHub Actions

[zdomke]

Reviewed this earlier. Found another way to fix the issue with @YektaY and made the changes on his branch (with his permission).

Works for me.