introduce namespace context manager

src/pystencilssfg/composer/basic_composer.py

src/pystencilssfg/context.py

src/pystencilssfg/generator.py

src/pystencilssfg/ir/entities.py

tests/generator_scripts/source/BasicDefinitions.py

tests/generator_scripts/source/Conditionals.py

tests/generator_scripts/source/JacobiMdspan.py

tests/generator_scripts/source/MdSpanFixedShapeLayouts.py

tests/generator_scripts/source/MdSpanLbStreaming.py

tests/generator_scripts/source/ScaleKernel.py

tests/generator_scripts/source/StlContainers1D.py

tests/generator_scripts/source/SyclBuffers.py

tests/integration/cmake_project/GenTest.py