Refactors the `CalculationFilterGroup` class to utilize C# primary constructors and property initializers, improving conciseness and readability.
The `IsValid()` method's logic is updated. Previously, it returned true if *any* filter in the group was valid. Now, it returns true only if *all* filters are valid, and an empty filter group is considered valid. This adjustment clarifies the group's validity criteria, aligning with common interpretations for `All` operations and addressing related technical debt.
Thom Lamb