Add Excel sheet SDK actions

[zizhengtai]

Summary

• add Excel sheet extension action models and traces to narada-core
• add read_excel_sheet and write_excel_sheet helpers to narada and narada-pyodide windows
• add an Excel sheets example mirroring the Google Sheets example

Tests

• .venv/bin/ruff check packages/narada-core/src/narada_core/actions/models.py packages/narada-core/src/narada_core/models.py packages/narada/src/narada/window.py packages/narada-pyodide/src/narada/window.py examples/excel_sheets.py
• .venv/bin/ruff format --check packages/narada-core/src/narada_core/actions/models.py packages/narada-core/src/narada_core/models.py packages/narada/src/narada/window.py packages/narada-pyodide/src/narada/window.py examples/excel_sheets.py
• .venv/bin/python -m py_compile packages/narada-core/src/narada_core/actions/models.py packages/narada-core/src/narada_core/models.py packages/narada/src/narada/window.py packages/narada-pyodide/src/narada/window.py examples/excel_sheets.py
• PYTHONPATH=packages/narada-core/src:packages/narada/src .venv/bin/python - <<'PY'
  from narada_core.actions.models import ReadExcelSheetRequest, WriteExcelSheetRequest
  read = ReadExcelSheetRequest(workbook_url='u', range='Sheet1!A1', microsoft_account_email='person@example.com')
  write = WriteExcelSheetRequest(workbook_url='u', range='Sheet1!A1', microsoft_account_email='person@example.com', values=[['a']])
  assert read.model_dump()['name'] == 'read_excel_sheet'
  assert write.model_dump()['name'] == 'write_excel_sheet'
  print('ok')
  PY