This change adds support for `bool_dtype`, `int_dtype`, `float_dtype`, and `string_dtype` parameters to the `to_geodataframe` method in `RowIterator` and `QueryJob`.

These parameters allow you to specify the desired pandas dtypes for boolean, integer, float, and string columns when converting BigQuery results to GeoDataFrames.

The changes include:
- Updating `RowIterator.to_geodataframe` to accept and pass these dtype parameters to the underlying `to_dataframe` method.
- Updating `QueryJob.to_geodataframe` to accept and pass these dtype parameters to the underlying `RowIterator.to_geodataframe` method.
- Adding unit tests to verify the correct handling of these parameters.