[WIP] Fix Runningvalue error with scope in function

[Copilot]

Fix for RunningValue function scope parsing issue

• Understand the issue - RunningValue function with scope parameter fails with "scope must be a constant" error
• Locate the bug in Parser.cs - scope detection logic incorrectly identifies the aggregate function as the scope for RunningValue
• Implement fix to handle RunningValue's unique 3-parameter structure (expression, aggregateFunction, scope)
  • Skip first comma when detecting scope for RunningValue (between expression and aggregate function)
  • Skip DataSet scope validation for RunningValue as it typically uses group names, not DataSet names
• Build and validate the fix - builds successfully
• Create tests for RunningValue with and without scope parameter
• Run tests to ensure no regressions - all RunningValue tests pass
• Verify with example file (DrilldownTest.rdl) - successfully parses without error
• Run codeql_checker to verify security
• Document the changes

Original prompt

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This section details on the original issue you should resolve

<issue_title>Runningvalue always give error with scope</issue_title>
<issue_description>Hi.

I try to use the Runningvalue function, but always give the same error : failed to parse: Sum function´s scope mut be a constant. I try different scope names , no luck :

=Runningvalue(Fields!debito.Value,Sum,cuenta)
=Runningvalue(Fields!debito.Value,Sum,Details_cuenta)
=Runningvalue(Fields!debito.Value,Sum,"cuenta")
=Runningvalue(Fields!debito.Value,Sum,"Details_cuenta")
=Runningvalue(Fields!debito.Value,Sum)

My group is called cuenta.

I am doing something wrong?

PD : Example provided in the package gives me the same error.
Thanks
</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #144

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