Implement phase 4 critical table imports

src/RolemasterDb.ImportTool/Parsing/ParsedCriticalCellArtifact.cs

@@ -1,6 +1,7 @@
 namespace RolemasterDb.ImportTool.Parsing;
 
 public sealed class ParsedCriticalCellArtifact(
+    string? groupKey,
     string rollBandLabel,
     string columnKey,
     IReadOnlyList<string> lines,
@@ -8,6 +9,7 @@ public sealed class ParsedCriticalCellArtifact(
     string descriptionText,
     string? rawAffixText)
 {
+    public string? GroupKey { get; } = groupKey;
     public string RollBandLabel { get; } = rollBandLabel;
     public string ColumnKey { get; } = columnKey;
     public IReadOnlyList<string> Lines { get; } = lines;