feat(normalizer): add generation parser to persons_tree

tools/import-normalizer/persons_tree.py

@@ -66,3 +66,11 @@ def _parse_year(raw: str | None) -> int | None:
                 return d.year
 
     return None
+
+
+def _parse_generation(raw: str | None) -> int | None:
+    """Extract the generation integer from column A values like 'G 3', 'G3', 'G  0'."""
+    if not raw:
+        return None
+    m = re.search(r"\d+", str(raw))
+    return int(m.group()) if m else None

tools/import-normalizer/tests/test_persons_tree.py

@@ -59,3 +59,27 @@ def test_parse_year_bare_out_of_range_year_is_none():
     # parse_date("1023") parses it as year 1023 (out of 1700-2100 guard).
     # The serial branch must NOT re-interpret it as a serial.
     assert persons_tree._parse_year("1023") is None
+
+
+def test_parse_generation_space():
+    assert persons_tree._parse_generation("G 3") == 3
+
+
+def test_parse_generation_no_space():
+    assert persons_tree._parse_generation("G3") == 3
+
+
+def test_parse_generation_extra_spaces():
+    assert persons_tree._parse_generation("G  0") == 0
+
+
+def test_parse_generation_trailing_garbage():
+    assert persons_tree._parse_generation("G 2         de Gruyter") == 2
+
+
+def test_parse_generation_empty():
+    assert persons_tree._parse_generation("") is None
+
+
+def test_parse_generation_none():
+    assert persons_tree._parse_generation(None) is None