Bug: Invisible gizmo can still transform

[ffrank913]

1. Why is this change necessary?

Because you could still transform a selected object via the gizmo even if it is hidden.

2. What does this change do, exactly?

It disables the tool's raycaster completely by disabling all bitmask layers.

We also added CodeCov to the project to take a look at the code coverage. This has no impact on the bug fix.

3. Describe each step to reproduce the issue or behaviour.

Select an object.
Make sure the gizmo is attached and visible.
Hide the gizmo.
Click at the position one of the axis was before and drag.
The object should NOT move.

4. Please link to the relevant issues (if any).

5. Checklist

• I have rebased my changes to remove merge conflicts
• I have written tests and verified that they fail without my change
• I have written or adjusted the documentation according to my changes
• This change has comments for package types, values, functions, and non-obvious lines of code
• I have read the contribution requirements and fulfil them.

[codecov-commenter]

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