fix: Fix scalar variables not applying after re-selecting a part colored by a vector component

[LKasianAnsys]

Issue

Addresses #23

Context

User story 3.5 (#23) of the remote rendering epic sees the variable ownership and color lookup table move from the client to the server. This PR fixes a pre-existing bug (described in the summary below) when coloring by a component of a vector or tensor variable.

To test:

• start VISOR with a variable that has a vector variable
• select a part and color by the vector variable (e.g. normals), and select one of the components (e.g. 'x').
• with the same part selected, color by a scalar variable
• success -> the scalar variable is correctly applied. fail -> unable to color by the scalar variable, or it does not apply the new color correctly on the mesh.

Copilot summary

This pull request addresses an issue where scalar variables were not being correctly applied after re-selecting a part that was previously colored by a vector component. The changes ensure that, upon re-selection, the correct variable component is chosen, defaulting to the first available option when necessary. The logic for resolving the displayed component was refactored and better tested, and new tests were added to verify the fix.

Bug fix:

• Fixed the logic so that scalar variables are now correctly applied after re-selecting a part colored by a vector component, by ensuring the appropriate component option is chosen or defaulting to the first option if the previous selection is invalid. [1] [2] [3]

Refactoring and improved logic:

• Extracted and documented logic for resolving the node's component ID into a new static method #resolveNodeComponentId in AggregateVariableInfo, improving clarity and maintainability.

Testing improvements:

• Updated and expanded tests to verify that the component selection falls back to the first option when a displayed component is invalid, and to ensure no warnings are emitted in this case. [1] [2]
• Added a new test to confirm that a scalar variable is correctly applied after re-selecting a part previously colored by a vector component.
• Added test utilities for interacting with select elements in the UI, used in new and updated tests.

[ansBAkula]

Tested and works. One small improvement (non functional): we could probably avoid showing the "Component" label and the associated dropdown showing up as "Magnitude" for scalar fields.

[LKasianAnsys]

@ansBAkula Yes agreed, nice suggestion. I've added it as an issue (#156) under the UI work feature.