v0.4.0

• Breaking change release.
• Updated to DuckDB 1.5.1.
• Removed the old %Duckdbex.Config{} config API.
• Replaced the old %Duckdbex.Config{}-based config layer with NIF-backed DBConfig resources.
• Added Duckdbex.create_config/0, Duckdbex.set_config_option/3 and Duckdbex.get_config_options/0.
• Duckdbex.get_config_options/0 now exposes the config options reported by DuckDB directly.
• Updated tests and README to document the new config model.
• Merged the @arthurbailao PR fix: correct NIF resource lifecycle and C++ initialization