feat(sedona-gdal): add convenience facade and mem builder

[Kontinuation]

Summary

• add the high-level Gdal facade and with_global_gdal convenience entry point
• add the MEM dataset builder on top of the lower-level dataset and raster wrappers
• keep the top-level API explicit by importing concrete raster/vector modules instead of relying on wrapper re-export aliases

Depends on #698.

Testing

• cargo test -p sedona-gdal
• cargo clippy -p sedona-gdal -- -D warnings