…ts, list_dashboards

LLMs consistently passed flat kwargs (search, page, page_size) to list_*
tools instead of wrapping them in the required `request` object, causing
pydantic validation errors.

- Add docstring usage examples to list_datasets, list_charts, and
  list_dashboards showing the correct `request={...}` call shape and
  explicitly warning against flat kwargs
- Enumerate valid filter columns directly in DatasetFilter, ChartFilter,
  and DashboardFilter field descriptions (e.g. `created_by_fk` is not a
  valid dataset filter col)
- Add TestListDatasetsRequestWrapper tests covering: correct request
  wrapper usage, default values, valid/invalid filter col validation,
  and the flat-kwargs rejection scenario from story #105712
- Allow E501 in list_*.py tool files (docstring examples need full request
  shapes to be instructive)

- Fix test_sortable_columns_in_docstring: assertion used plain-text match
  but docstring now uses RST backtick format; use substring check for both
  'Sortable columns for' and 'order_column' separately
- Fix test_dataset_filter_valid_col: opr='ct' is not a valid
  ColumnOperatorEnum value; use opr='sw' (starts-with) instead
- Add test_request_wrapper_enforced_by_tool: exercises the wrapper pattern
  through the actual FastMCP client call (not just schema instantiation),
  verifying the MCP tool layer accepts request={...} correctly
- Strengthen test_flat_kwargs_rejected: assert that the ToolError message
  references the unexpected arguments ('search', 'Unexpected', or 'request')
  so the test cannot pass on unrelated failures

…oard docstring test

- Replace opr:"ct" with opr:"sw" in filter examples in list_datasets,
  list_charts, and list_dashboards docstrings — "ct" is not a valid
  ColumnOperatorEnum value, so examples using it produce validation errors
- Fix TestDashboardSortableColumns.test_sortable_columns_in_docstring:
  assertion checked for "Sortable columns for order_column:" (plain text)
  but docstring uses RST backtick format; split into two substring checks
  matching "Sortable columns for" and "order_column" separately

…port

All 6 new test methods in TestListDatasetsRequestWrapper were missing
the required -> None return type annotation (Rule 12). Also remove the
inline `from fastmcp.exceptions import ToolError` in test_flat_kwargs_rejected
since ToolError is already imported at module top-level (line 27).