Make internal types and functions private

Make implementation details private to reduce the public API surface:

In filesystem.rs:
- RealBasicFileSystem and FakeBasicFileSystem structs
- Their inner fields
- parse_indented_file_system_string function

In import_scanning.rs:
- py_found_packages_to_rust function
- get_modules_from_found_packages function
- scan_for_imports_no_py function
- to_py_direct_imports function

Only the Python-facing wrapper structs (PyRealBasicFileSystem,
PyFakeBasicFileSystem) and the exported Python functions remain public.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Peter554

rust/src/filesystem.rs

@@ -30,13 +30,13 @@ pub trait FileSystem: Send + Sync {
 
 #[derive(Clone)]
 #[pyclass]
-pub struct RealBasicFileSystem {}
+struct RealBasicFileSystem {}
 
 // Implements a BasicFileSystem (defined in grimp.application.ports.filesystem.BasicFileSystem)
 // that actually reads files.
 #[pyclass(name = "RealBasicFileSystem")]
 pub struct PyRealBasicFileSystem {
-    pub inner: RealBasicFileSystem,
+    inner: RealBasicFileSystem,
 }
 
 impl FileSystem for RealBasicFileSystem {
@@ -184,14 +184,14 @@ impl PyRealBasicFileSystem {
 type FileSystemContents = HashMap<String, String>;
 
 #[derive(Clone)]
-pub struct FakeBasicFileSystem {
+struct FakeBasicFileSystem {
     contents: Arc<Mutex<FileSystemContents>>,
 }
 
 // Implements BasicFileSystem (defined in grimp.application.ports.filesystem.BasicFileSystem).
 #[pyclass(name = "FakeBasicFileSystem")]
 pub struct PyFakeBasicFileSystem {
-    pub inner: FakeBasicFileSystem,
+    inner: FakeBasicFileSystem,
 }
 
 impl FakeBasicFileSystem {
@@ -319,7 +319,7 @@ impl PyFakeBasicFileSystem {
 /// Parses an indented string representing a file system structure
 /// into a HashMap where keys are full file paths.
 /// See tests.adaptors.filesystem.FakeFileSystem for the API.
-pub fn parse_indented_file_system_string(file_system_string: &str) -> HashMap<String, String> {
+fn parse_indented_file_system_string(file_system_string: &str) -> HashMap<String, String> {
     let mut file_paths_map: HashMap<String, String> = HashMap::new();
     let mut path_stack: Vec<String> = Vec::new(); // Stores current directory path components
     let mut first_line = true; // Flag to handle the very first path component

rust/src/import_scanning.rs

@@ -34,7 +34,7 @@ impl<'py> FromPyObject<'py> for DirectImport {
     }
 }
 
-pub fn py_found_packages_to_rust(py_found_packages: &Bound<'_, PyAny>) -> HashSet<FoundPackage> {
+fn py_found_packages_to_rust(py_found_packages: &Bound<'_, PyAny>) -> HashSet<FoundPackage> {
     let py_set = py_found_packages
         .downcast::<PySet>()
         .expect("Expected py_found_packages to be a Python set.");
@@ -52,7 +52,7 @@ pub fn py_found_packages_to_rust(py_found_packages: &Bound<'_, PyAny>) -> HashSe
     rust_found_packages
 }
 
-pub fn get_modules_from_found_packages(found_packages: &HashSet<FoundPackage>) -> HashSet<Module> {
+fn get_modules_from_found_packages(found_packages: &HashSet<FoundPackage>) -> HashSet<Module> {
     let mut modules = HashSet::new();
     for package in found_packages {
         for module_file in &package.module_files {
@@ -73,7 +73,7 @@ fn module_is_descendant(module_name: &str, potential_ancestor: &str) -> bool {
 /// Statically analyses the given module and returns a set of Modules that
 /// it imports.
 #[allow(clippy::borrowed_box)]
-pub fn scan_for_imports_no_py(
+fn scan_for_imports_no_py(
     file_system: &Box<dyn FileSystem + Send + Sync>,
     found_packages: &HashSet<FoundPackage>,
     include_external_packages: bool,
@@ -169,7 +169,7 @@ fn scan_for_imports_no_py_single_module(
     Ok(imports)
 }
 
-pub fn to_py_direct_imports<'a>(
+fn to_py_direct_imports<'a>(
     py: Python<'a>,
     rust_imports: &HashSet<DirectImport>,
 ) -> Bound<'a, PySet> {