adds show-build-env command

justfile

@@ -68,4 +68,10 @@ release-prep: verify-clean-git pre-release
 release: release-prep
     git tag "v$(just get-crate-version)"
     git push && git push --tags
-    
+   
+# diagnostic command for viewing value of build variables at runtime 
+show-build-env:
+    @echo "registry-backup v$(just get-crate-version)"
+    @echo "rustc-version={{rustc-version}}"
+    @echo "publish-registry={{publish-registry}}"
+    @env | rg RUST --color never