fix: AppBio QuantStudio Design & Analysis - Check for valid rq values before setting r_sample and r_target

[slopez-b]

No description provided.

[Copilot]

Pull request overview

This PR improves robustness of the AppBio QuantStudio Design & Analysis Relative Standard Curve parser by avoiding reference-sample/target inference when the RQ sheet has no usable Rq values, preventing conversion failures in those scenarios.

Changes:

• Added _has_valid_rq_values() to detect whether the “RQ Replicate Group Result” sheet contains any non-null Rq values before attempting reference inference.
• Updated RelativeStandardCurveCreator.create() to set reference_sample/reference_target to None when no valid Rq values exist.
• Relaxed the type of r_sample in iter_relative_standard_curve_calc_docs() to allow None.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/allotropy/parsers/appbio_quantstudio_designandanalysis/structure/relative_standard_curve/creator.py	Adds an RQ validity check and conditionally skips reference inference to avoid runtime errors.
src/allotropy/parsers/appbio_quantstudio_designandanalysis/appbio_quantstudio_designandanalysis_calculated_documents.py	Updates iter_relative_standard_curve_calc_docs signature to accept `r_sample: str

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