init. core algorithm, initial testing, basic cli.

test/test_rcvs.py

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+import polars as pl
+from smithy import smith_set
+
+def test_condorcet():
+    df = pl.DataFrame({
+                          'A': [1, 1, 2, 1],
+                          'B': [2, 2, 1, 2],
+                          'C': [3, 3, 3, 3],
+                      })
+    assert smith_set(df) == ['A']
+
+def test_rockpprscrcycle():
+    df = pl.DataFrame({
+                             'A': [1, 2, 3],
+                             'B': [2, 3, 1],
+                             'C': [3, 1, 2],
+                         })
+    assert smith_set(df) == ['A', 'B', 'C']
+
+def test_abpair():
+    df = pl.DataFrame({
+        "A": [1, 2, 1, 3],
+        "B": [2, 1, 3, 1],
+        "C": [3, 3, 2, 2]
+        })
+    assert smith_set(df) == ['A', 'B']
+
+def test_fourcycle():
+    df = pl.DataFrame({
+        "A": [1,2,3,4],
+        "B": [2,3,4,1],
+        "C": [3,4,1,2],
+        "D": [4,1,2,3],
+    })
+    assert smith_set(df) == ['A', 'B', 'C', 'D']