feat: add CLI options for custom CSV separator and normalize-to-one branch normalization

tests/physics/test_multi_branch.py

@@ -460,8 +460,8 @@ class TestMultiBranchCSVExport:
 
         import pandas as pd
 
-        # Read CSV (skip comment headers, use tab delimiter)
-        df = pd.read_csv(csv_path, comment="#", sep='\t')
+        # Read CSV (skip comment headers, use comma delimiter by default)
+        df = pd.read_csv(csv_path, comment="#", sep=',')
 
         # Should have total spectrum column
         assert "total_spectrum" in df.columns
@@ -500,7 +500,7 @@ class TestMultiBranchCSVExport:
 
         import pandas as pd
 
-        df = pd.read_csv(csv_path, comment="#", sep='\t')
+        df = pd.read_csv(csv_path, comment="#", sep=',')
 
         assert "total_spectrum" in df.columns
         assert "branch_1_spectrum" in df.columns