feat: ExcelParser 基础（workbook/sheet 读取 + source_uri）

tests/excel_helpers.py

@@ -0,0 +1,20 @@
+from openpyxl import Workbook
+
+
+def new_workbook(sheets: dict[str, list[list]]) -> Workbook:
+    """生成临时 Workbook：key=Sheet 名，value=grid（cell 值）。"""
+    wb = Workbook()
+    wb.remove(wb.active)
+    for name, grid in sheets.items():
+        ws = wb.create_sheet(name)
+        for r, row in enumerate(grid, start=1):
+            for c, value in enumerate(row, start=1):
+                ws.cell(row=r, column=c, value=value)
+    return wb
+
+
+def save_workbook(tmp_path, wb: Workbook) -> str:
+    """落盘到 tmp_path 并返回路径字符串。"""
+    path = tmp_path / "source.xlsx"
+    wb.save(path)
+    return str(path)