add missing expected files list in test_dir_circular_dependencies_impl

add test_dir_circular_dependencies_impl_cmake testcase

add testcase test_dir_simple_cmake which runs cmake with clang-20, clang-21, gcc-15

circular dependencies in implementation units without partitions

add assert on cycle

find circular dependencies between modules

refactoring: extract `FileProcessingState`

refactoring: _add builder methods

refactoring joint builder for nicer architecture

joint modules: allow having header named the same way as joint module

refactoring: `ModuleInterfaceUnitBuilder` has `partititons` now and adds them to module content in `build_result()` instead of `create_joined_module_files()`

refactoring joint builder for nicer architecture

refactoring: `get_module_name_for_import()` to `ModuleFilesResolver`

refactoring: `filename_to_module_name()` moved to `FilesResolver`

doc: actualize usage

doc: assumptions are configurable

doc: add `--join` argument