Replace pandas with a small openpyxl/csv reader for imports.

pandas + numpy were ~60MB of the shipped venv for three call sites (alarm
Excel import, managed-NE import, import template). netx_api/tabular.py
reads/writes xlsx and csv and parses spreadsheet timestamps.

Checked against the pandas version on the same inputs: timestamp parsing
identical for 24 formats, managed-NE csv/xlsx import, stored rows and both
templates identical. Differences, all fixes:
- alarm codes in mixed text/number columns are "1001", not "1001.0"
- error row numbers are the real sheet rows (blank rows no longer shift them)
- GBK-encoded CSVs (Chinese Excel "Save as CSV") import instead of failing
- "2024年1月2日 03:04:05" style timestamps parse

Also: conftest compares parsed DB URLs (newer SQLAlchemy renders "C:" as
"C%3A").

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_tabular.py

@@ -0,0 +1,83 @@
+"""xlsx/csv helpers that replaced pandas in alarm + managed-NE imports."""
+import io
+from datetime import datetime, timezone
+
+from openpyxl import Workbook, load_workbook
+
+from netx_api.importer import _dt, _int, _str
+from netx_api.tabular import parse_datetime, read_csv, read_table, read_xlsx, write_csv, write_xlsx
+
+
+def _xlsx(rows):
+    wb = Workbook()
+    ws = wb.active
+    for r in rows:
+        ws.append(r)
+    buf = io.BytesIO()
+    wb.save(buf)
+    return buf.getvalue()
+
+
+def test_read_xlsx_types_blank_rows_and_sheet_row_numbers():
+    content = _xlsx([
+        ["Time", "Code", "Port", None, "Code"],
+        [datetime(2024, 1, 2, 3, 4, 5), 1001, 22.0, "x", "dup"],
+        [None, None, None, None, None],
+        ["  ", "A", 2.5, None, None],
+    ])
+    headers, rows = read_xlsx(content)
+    assert headers == ["Time", "Code", "Port", "Unnamed: 3", "Code.1"]
+    assert rows == [
+        (2, {"Time": datetime(2024, 1, 2, 3, 4, 5), "Code": 1001, "Port": 22, "Unnamed: 3": "x", "Code.1": "dup"}),
+        (4, {"Time": None, "Code": "A", "Port": 2.5, "Unnamed: 3": None, "Code.1": None}),
+    ]
+
+
+def test_read_csv_bom_quotes_short_rows_and_blank_lines():
+    content = "a,b,c\n1,\"x, y\",\n\n2\n".encode("utf-8")
+    headers, rows = read_csv(content)
+    assert headers == ["a", "b", "c"]
+    assert rows == [(2, {"a": "1", "b": "x, y", "c": None}), (4, {"a": "2", "b": None, "c": None})]
+
+
+def test_read_csv_falls_back_to_gbk():
+    headers, rows = read_csv("名称,地址\n核心,10.0.0.1\n".encode("gbk"))
+    assert headers == ["名称", "地址"]
+    assert rows == [(2, {"名称": "核心", "地址": "10.0.0.1"})]
+
+
+def test_read_table_dispatches_on_extension():
+    assert read_table(b"h\nv\n", "X.CSV") == (["h"], [(2, {"h": "v"})])
+    assert read_table(_xlsx([["h"], ["v"]]), "x.xlsx") == (["h"], [(2, {"h": "v"})])
+
+
+def test_write_csv_and_xlsx_round_trip():
+    csv_bytes = write_csv(["a", "b"], [[1, None], ["中文", "x"]])
+    assert csv_bytes.startswith("".encode("utf-8"))
+    assert read_csv(csv_bytes)[1] == [(2, {"a": "1", "b": None}), (3, {"a": "中文", "b": "x"})]
+
+    xlsx = write_xlsx([("import", ["a"], [[1]]), ("types", ["t"], [["x"], ["y"]])])
+    wb = load_workbook(io.BytesIO(xlsx))
+    assert wb.sheetnames == ["import", "types"]
+    assert read_xlsx(xlsx) == (["a"], [(2, {"a": 1})])
+
+
+def test_parse_datetime_formats():
+    want = datetime(2024, 1, 2, 3, 4, 5)
+    for text in (
+        "2024-01-02 03:04:05", "2024/01/02 03:04:05", "2024/1/2 3:04:05", "2024-1-2 03:04:05",
+        "2024-01-02T03:04:05", "01/02/2024 03:04:05", "20240102030405", "02-Jan-2024 03:04:05",
+        "Jan 02, 2024 03:04:05", "2024年1月2日 03:04:05",
+    ):
+        assert parse_datetime(text) == want, text
+    assert parse_datetime("2024-01-02T03:04:05Z") == datetime(2024, 1, 2, 3, 4, 5, tzinfo=timezone.utc)
+    assert parse_datetime("2024-01-02") == datetime(2024, 1, 2)
+    for bad in (None, "", "  ", "nan", "NaT", "abc"):
+        assert parse_datetime(bad) is None
+
+
+def test_importer_cell_helpers():
+    assert _dt("2024-01-02T03:04:05Z") == datetime(2024, 1, 2, 3, 4, 5)  # stored as naive UTC
+    assert _dt(float("nan")) is None and _dt("garbage") is None
+    assert _str(1001) == "1001" and _str(None) == "" and _str(" nan ") == "" and _str(" a ") == "a"
+    assert _int("7") == 7 and _int(2.0) == 2 and _int("x") == 0 and _int(None) == 0