fix(sonar): exclude test files from duplication checking

Test code intentionally contains similar patterns for comprehensive coverage.
SonarCloud's CPD (Copy-Paste Detection) should not flag test file duplication.

Author: leifj

sonar-project.properties

@@ -9,6 +9,10 @@ sonar.organization=sunet
 sonar.sources=.
 sonar.exclusions=vendor/**,**/testdata/**
 
+# Exclude test files from duplication detection
+# Test code intentionally contains similar patterns for comprehensive coverage
+sonar.cpd.exclusions=**/*_test.go
+
 # Go-specific settings
 sonar.go.coverage.reportPaths=coverage.out,didcomm_coverage.out