FIX: Hide Bin Count Setting for FormulaCurves

[zdomke]

Description

Fixes error with CurveSettingsModal. The widget would try to reference a non existent property for FormulaCurveItems. This PR adds a check to prevent referencing the property if it doesn't exist.

Motivation

The error below would come up when opening the settings for a Formula curve:

Traceback (most recent call last):
  File "/sdf/home/z/zdomke/workspace/trace/trace/trace/widgets/control_panel.py", line 968, in show_settings_modal
    self.pv_settings_modal = CurveSettingsModal(self.pv_settings_button, self.plot, self.source)
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/sdf/home/z/zdomke/workspace/trace/trace/trace/widgets/curve_settings.py", line 40, in __init__
    bin_count = curve.optimized_data_bins
                ^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'FormulaCurveItem' object has no attribute 'optimized_data_bins'

Screenshots

Curve Settings, includes line labeled "Optimized bin count":

Formula Curve Settings, does not include line labeled "Optimized bin count":

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