Refactor class hierarchy to avoid virtual inheritance

[wdconinc]

This PR removes the virtual inheritance support which was originally introduced to support multiple subsystem types:

classDiagram
    class VQwSubsystem {
        <<abstract>>
        +TString fSystemName
        +ProcessEvent()
        +operator=(VQwSubsystem*)
    }
    
    class VQwSubsystemParity {
        <<abstract>>
        +operator=(VQwSubsystem*) = 0
        +operator+=(VQwSubsystem*) = 0
        +FillDB()
        +Blind()
    }

    class VQwSubsystemTracking {
        <<abstract>>
        +operator=(VQwSubsystem*) = 0
    }

    class VQwDetectorArray {
        <<abstract>>
        +vector<QwIntegrationPMT> fIntegrationPMT
        +vector<QwCombinedPMT> fCombinedPMT
        +operator=(VQwSubsystem*)
        +operator+=(VQwSubsystem*)
    }
    
    class QwDetectorArray {
        +QwDetectorArray(name)
        +using VQwDetectorArray::operator=
    }
    
    class QwBlindDetectorArray {
        +Blind(QwBlinder*)
        +using VQwDetectorArray::operator=
    }

    class QwScanner {
        +QwScanner(name)
        +operator=(VQwSubsystem*)
        +operator+=(VQwSubsystem*)
        +FillDB()
        +Blind()
    }

    %% Virtual inheritance relationships
    VQwSubsystem <|-- VQwSubsystemParity : "virtual inheritance"
    VQwSubsystem <|-- VQwSubsystemTracking : "virtual inheritance"
    VQwSubsystemParity <|-- VQwDetectorArray : "virtual inheritance"
    
    %% Regular inheritance
    VQwDetectorArray <|-- QwDetectorArray : "public inheritance"
    QwDetectorArray <|-- QwBlindDetectorArray : "public inheritance"

    %% Show the diamond pattern being avoided
    VQwSubsystemParity <|-- QwDetectorArray : "virtual public (redundant)"
    VQwSubsystemParity <|-- QwBlindDetectorArray : "virtual public (redundant)"

    %% Show the diamond pattern being avoided
    VQwSubsystemParity <|-- QwScanner : "virtual public (redundant)"
    VQwSubsystemTracking <|-- QwScanner : "virtual public (redundant)"

    note for VQwSubsystemParity "Uses virtual inheritance\nto avoid diamond problem"
    note for QwDetectorArray "Uses 'using' declarations\nto expose base operators"
    note for VQwSubsystemTracking "Already removed"
    note for QwScanner "Already removed"

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Since we don't aim to support VQwSubsystemTracking anymore, we can get rid of the virtual inheritance entirely.